would a AMD Phenom II X4 940 Deneb and ASUS M4A79 Deluxe AM2+/AM2 AMD 790FX MB be a good gaming rig start?

I had in mind to go with an intell chip, the E8500 wolfdale but seeing AMD's prices for quads compared to intell made me think of changing and i would rather be ready for when games require more than dual processors.

Yes, those are decent parts. The 940 is comparble to the Q9400, and the M4A79 is a nice mobo for everything. And it's an Asus, so it must be excellent.

Yes this is a good start, The Phenom ii is an excellent AMD processor, and as you say the cost difference to go to the Intel is significant. Specially since the performance difference vs the cost is really hard to defend , unless you have no money concerns.

the x4 940 is a good cpu. It is on par with the q9400-q9550 and a system build would be considerably cheaper than a i7 build. I priced out a decent rig yesterday and came up with $800-$900 depending on what you want using the 940 deneb, ati 4870 and the 790gx board. Check the cache on the wolfdales....i think they are L2 4mb giving the cores 2mb each. The x4 940 has 6mb L3 giving each core <2mb per core, but only if you are using all 4....which is rare. The e8500 is a good bargain cpu too, though and it is an overclocking beast.