What files from Steam should I back up?

[Space Cowboy]

I'm going to re-install Steam and HL2 to see if it solves my memory crash problem (have the retail cd)
Is there any sort of files from steam I should back up before I uninstall the whole lot?

 

[BigDaz]

I don't think so. Everything it needs is saved online I think, remember your login and password though.