Getting Started
Before you start researching for a digital copier, ask yourself these three questions to get a good grasp of what your needs are.

1. What are my needs for an office copier?
Modern digital copiers are sometimes referred to as "multifunctional products" because they can do more than just copy. Almost all are also capable of printing, faxing, and scanning. Having a multifunctional product connected to your internal network allows your staff to print, copy, or send faxes from their computers.
Because the machine is still a copier, users can also make collated, even stapled, sets of documents without having to leave their seats. Some buyers have the perception that adding more functions to a copier can reduce its reliability, but that is not the case any more.
You also need to decide whether you need a copier that supports color. While color machines do not command the exorbitant premiums they used to, you will still pay 20% to 30% above the cost of a black and white copier.
For most businesses that need some color printing and/or copying, a black and white/color hybrid is the best choice. By switching between b&w and color modes, a hybrid copier can save you money in expensive color copier consumables. Dedicated graphic color machines are much more expensive, with the additional cost largely for print-quality accuracy in color reproduction and faster processors, neither of which is essential in the typical office.

2. What is my copy and print volume?
Once you decide on the features you need, the next step is to narrow your choices based on the number of copies you make in a month.
If you already own or lease a copier, you can determine your actual copier usage by looking at the counter. You can also use your monthly paper consumption to help determine your current copy and print volume. If you do not have a copier, examine your copy shop receipts to get a sense for your volume. If you are going to use the copier as a network printer, increase the figure by 30% to 50%.
Once you have a rough volume figure, increase it by at least 15%. This will help you account for future growth, as well as compensate for the somewhat inflated monthly copy volumes set by manufacturers for their models. Overworking an office copier is the quickest route to frustrating downtime and expensive service calls - better to pay for slightly more capacity than you need than risk damaging an expensive and essential piece of office equipment.
If you are expecting to make fewer than 700 copies a month, you probably do not need the expense of a "business" copier. You would be better off purchasing a small office copier from an office superstore - unless you want the advanced features or service guarantees that come with business copiers.

Copier speed is measured in copies per minute (cpm).  CPM refers to the number of letter-sized pages the machine can produce in one minute when running at full speed. The copier industry defines six segments:

Segment 1 machines will quickly frustrate you with slow copy times unless you operate a very small office or work out of your home. Generally, most companies will be satisfied with copiers from Segments 2, 3 and 4. Segment 3 and 4 copiers tend to have more features and are suited for networked use. Unless you have extremely large copy volumes, a segment 5 or 6 copier is overkill.

Basic Copier Features

An automatic document feeder (ADF) or re circulating document feeder (RADF) allows you to copy multi-page documents without having to lift and lower the cover for every sheet you copy. Instead, you drop a stack of originals (up to 50 pages or 100 pages) into the office copier feeder, press start, and the ADF automatically pulls each page through. 

Digital copiers can sort copied sets electronically without the use of sorter bins. Instead of separate bins, the copies are placed in a single tray at a right angle or offset from each other, allowing you to easily identify where one set ends and another begins. Bin-free sorting allows you to make unlimited sets at one time, rather than only as many sets as you have sorter bins.
You may want a finisher if you want your office copier to copy many sets of multi-page documents. The most familiar type of finisher is the automatic stapler, which can be a huge time-saver. More advanced versions include three-hole punches, saddle stitch binding, folding, and more. Finishers are optional on many machines, and usually carry an additional cost.

Each paper tray, cassette, pedestal, or paper feed unit is a separate paper source. The number of sources is important if you want to be able to copy onto different paper stocks, such as letterhead, legal size stock, or transparencies, without reloading the machine. Paper sources typically hold a minimum of 50 to 100 sheets, and the largest-capacity units can hold up to 3,000 sheets.
Typically, office copiers include at least one fixed-size and a couple of adjustable-size paper trays. Unfortunately, heavy paper stock often jams if you load it into a standard paper tray. To get around this problem, most copiers include a bypass tray, a special tray that provides a straight paper path for heavy paper and labels.

Advanced Copier Features

Capabilities that used to be expensive or simply not available are now standard on today's digital multifunction devices. Remember that you can upgrade many of these features later - if you choose the right copier.
Some machines can be upgraded with a "plug and play" type of upgrade, while others require more extensive hardware fixes. If you are considering adding printing or faxing modules later, ask about the specifics of the upgrade process.

Printing

Add a printer module and network card to a digital copier and it can double as an office laser printer, working at the same speed it makes copies. A copier can allow your employees to produce dozens of stapled copies of a five-page, two-sided proposal - without leaving their desks. Most offices can benefit from using a copier as a printer as per-page costs can be as little as 20% of laser printer printing costs.
Most copiers run standard networking protocols, but you still need to make sure the model you choose is compatible with your network. Involving your IT department in this aspect of the copier purchase decision up front can save you significant headaches later.

With the addition of a fax module, you can send and receive faxes through the copier. You can easily send multi-page faxes using the document feeder, or you can use the copier glass to fax single pages or parts of books or catalogs. Incoming faxes printed as they're received, sometimes into a separate output tray. With a network interface, users can even send faxes from their computers.

Digital copiers can edit your documents while duplication is happening. This can include automatic page numbering, adding watermarks such as "confidential" or "copy", or adding date stamps. They can rotate scanned images to match the orientation of the available paper supply, saving on wasted time and paper from unanticipated errors.
They can also combine images in creative ways, such as copying a two-sided original - say, a check - onto one page, or reducing and combining originals to put 2, 4, or 8 pages onto one.

Digital copiers with enough memory can support stackless duplexing by storing each side of the original page in memory, then printing both sides of the copy. This means the number of two-sided copies you make is no longer limited by the capacity of a duplex tray. You will get your duplexed copies much faster, too.

Digital copiers usually offer an automatic sizing function on their machines. This enables the copier to note the dimensions of your original document and adjust itself using preset reduction/enlargement settings, even if your copying paper is a different size than your original.

Almost all copiers now have an automatic shut-off option - it saves energy and decreases wear on a copier by turning the machine off if it has not been used for a set period of time.

Many digital copiers allow you to require that users enter a code before they can make copies. This provides a level of security - preventing unauthorized usage - as well as allowing you to analyze current usage patterns by department. Some machines can also hold faxes or network documents in memory until the correct code is entered then print them. This prevents confidential documents from being left in the output tray for any passerby to view.