Buying DIrect Download

Steam

http://store.steampowered.com/

Steam

http://store.steampowered.com/

somegtalover

Seconded.

Steam, like the guy above mentioned is a good one. Here are two more options

Direct 2 Drive, they store your games on their server for as long as they are up and running http://www.direct2drive.com/

Good Old Games, cheap games only purchased one so far, but worked well and they have a good catelog for old games http://www.gog.com/en/frontpage/

Steam and direct 2 drive only ones i use and never had any problems and steam does an insane sale every summer and every winter.

Steam and direct 2 drive only ones i use and never had any problems and steam does an insane sale every summer and every winter.

Sleepyz

GOG

Steam

Impulse

GamesGate

Direct2Drive

All the ones I know of. Hope that helps. :)