Where to locate power outlets on server rack?

If you're talking about 4-post cabinets: I like vertical PDUs inside the sides of the rack. I place them half-way up the height of the rack and coil excess power cords in the side panels. Normally the UPSs are at the bottom of the rack (where they really should be), plugged into mains outlets that are either under the floor or at floor level. The UPSs feed the PDUs, and the PDUs feed the servers and other equipment.

On 2-post racks: I like rack-mounted horizontal power strips staggered throughout the rack. The same is true for the UPSs and electrical receptacles-- they're at the bottom and feed the power strips in the rack. I coil the power cords on one side of the rack in the vertical cable management (and network cables on the other size). Increasing, though, I'm using Neatpatch cable management and have less and less need for vertical cable management.

The way your question sounds, I'd get the electrician to put your outlets right at floor level roughly in the middle of the rack footprint, put the UPSes a bit above that so that you have room to coil the cords for the UPSes on the ground. Then go with what Evan suggested and mount PDUs in the middle (vertically) of the rack.

In our case, we had a raised floor with the racks in the middle of the room and a 6-foot built-in table right next to the racks, so our electrician ran our lines in raceways along the back of the table.

If the racks are deep enough, perhaps consider "0 U" vertical PDUs mounted at the back of the cabinet.

With enough space in the back of the rack, these don't interfere too much with data cable management.

Something like this: http://pc.pcconnection.com/1/1/7992-apc-power-distribution-unit-metered-rm-0u-30a-120v-24-5-20-outlets-ap7832.html

Any amount of raised floor helps as well since the electrical conduit can come up under the rack and the PDUs (and slack cord) can be done under a floor tile but it doesn't sound like you have this option.

If none of that is an option, bottom of the rack would be preferable in my opinion to power at the top of the rack.