Are you OC'ing? If so, I think Intel is the way to go either way. Since the DDR2/3 price differences are negligible and the CPUs are close, mobo's are close, try for the i5. Might be worth waiting until the AMD Phenom IIx6 comes out an benches too if you have time to wait.
If the i7s come into play, then the i7 860 is probably the best option for rendering. If you're using huge files, then the i7 920 has a slight benefit from the triple channel memory. The i7s should still beat the unreleased x6s.