What's the best memory module for gamming???

I plan to spend about 150$ canadian on 2x512mb or 1gig of ram...

My specs a
a amd athlon 64bits 3200 on a asus board nf4 a8n5x with a memory
controller that support 50ns 60ns 70ns memory speed.

I would prefer to get the lowest timming as possible as it is known to
best perform on amd os

And i would like to know if there is alot of difference between 1gig
of low cost memorys vs expensive one.

Ie: the goods and the cons, beside garantie,reliability and brands.


TY.