It may sound trivial, as functionality is paramount, but don't dismiss the importance of appearance. When you bring the CEO of one your customers through your facility to help seal a large deal, racks made of kiln-dried two-by-fours and plywood won't inspire confidence.
And buying all your racks from a single vendor may be your best bet: You can use extra mounting hardware from new racks elsewhere; cabinets will be all the same size; and you can apply the lessons learned from previous rack installations to new ones.
Functional and Secure
Best practices dictate that, in addition to a limited-access data center, rack fronts and backs should be restricted to authorized personnel. If you select a rack with removable side panels, make sure there is a lock or other mechanism to secure those panels. Troublemakers with a mind to kick out cables or power-off servers may be deterred if denied access to the machines. If your IT infrastructure is too small to justify a dedicated server room, a locking equipment rack may suffice.
For added security, you can buy a sensor to monitor the doors, temperature, humidity and voltage conditions in each rack. For the rack that has everything, we like NetBotz RackBotz and WallBotz sensors. We tested the WallBotz a year ago (see "NetBotz WallBotz 400 Is the Next Best Thing to Being There") and found it so efficient for room monitoring that we use one in our NWC Inc. lab (see our NetBotz monitoring system in action at inc.networkcomputing.com).
Investigate the rack's power-distribution system. Unsightly and unsafe six-plug power strips from Wal-Mart wire-tied to the back of your racks aren't going to impress the fire inspector or a perspective customer. An emerging trend coming from telecommunications technology is the use of DC-driven devices at 24 or 48 volts. Server vendors offer these options, and smart companies are using them to provide a single power system for all their data-center devices. If you want to take advantage of this opportunity, make sure your current racks can take such an upgrade without ugly third-party hacks.