You have 2 options really:
AMD Athlon II X2 + AM3 785/790/etc.
Intel Core i3-530 + H55 Motherboard (These new i3 chips have the GPU built into them.
Both are great for displaying HD content in a HTPC situation, however gaming will be very limited.
DDR3 RAM is the same price as DDR2 RAM now, plus DDR2 RAM is outdated and if you follow either of the paths I listed above, DDR3 is required.