(A) Lease vs. Buy: If you can swing it, lease them instead - tax benefits, etc.
(B) Do you really need 8 cores per box? I.e., you can get used dual-dual machines a lot cheaper than 50% of the price of the dual-quad machines.
(C) If you know what you want and are buying new then going with a white box builder is significantly cheaper than buying from Dell/HP/etc. I've been pretty happy with ASA especially since they've delivered/picked-up/serviced machines directly to/from/in our colo but there are plenty of decent vendors and they most end up using SuperMicro-based systems anyways.
(D) Do you really need 1U? Why? Power/cooling issues are putting more constraints on things than size at many places and a 2U is often cheaper, more flexible, fixable, etc.
(E) Really knowing exactly what you want can make a big difference in talking with the salespeople. Buying at the end of the quarter is a good thing if you can swing it.
(F) More ram is more better and 32GB is the current sweet spot in terms of lots of memory for a good price. Pay particular attention to the motherboards that you're considering as there can be a price premium at the various steps depending on if you need the flexibility to upgrade the memory a lot later.
(G) You mention that disk isn't much of a concern. Is that because you just want lots of compute nodes or because you're putting everything into a NAS/SAN or what?