Not really. It depends on what parts you want. Right now, the older Socket A setups will be cheaper, simply because they're old news, while Socket 939 systems are going to be fairly pricey because they're pretty new.

There's really no 'season' for PC stuff, but since Christmas is coming up, you can expect to see some deals on some items. But, then again, that's pretty universal, no matter what the goods are.