Don't bother buying FPGAs right now at all (unless you're going bfl and getting the upgrades purchased at the same time).

I'd look at picking up some 7990 ( or 7970x2 ) cards. Should be able to get between 1gh/s and 1.4gh/s. Then run them until asics are out and the difficulty shoots up - at the point where you see a 50% loss in btc generation, then you should sell the cards (should have held 80-90% of value) and purchase asic product.

If you'd rather not rig them yourself --- let me know - I'd be happy to assemble, custom cool, overclock and ship to you.