I've had astoundingly good service and prices from
www.sprocketcenter.com -- they are in LA and know their stuff.
For chains I use a DID ERV3 for 520 applications and a DID 530ZVMX for 530 applications. I generally use steel sprockets (usually the stealth/super-sprox ones with the aluminum carrier) except on light weight race bikes which get all-aluminum (make sure its good, 7075 series aluminum if you want more than a day out of it). I prefer 530 chains on street bikes as they seem to last so long -- I generally go 40k miles and I'm not much on chain maintenance and ride every day, rain, snow or shine.