I would use dropbox for that. The problem is that every game seems to use different places to store savefiles. Some are in the My Documents folder, some are not, so you might have to search a little to find what you are looking for. But once you have the saves, uploading them to dropbox is easy:)
I think you can just copy your entire game to a portable HDD and copy it to the regular location where Steam installs its games. Just verify files afterwards. Anyway, the backup took about 18 hours for me for about 60GB of games, which is insane. And now I lost my Mass Effect 1&2 saves since it doesn't back-up saves. The Steam backup is the only thing Valve didn't do right in Steam.
@sander_dutch: Steam backup backs up the game install, not the save files. I wish Steam would know where they installs and configs for each game are and backs up that as well. Someday...
Like sander_dutch says, the saves could be anywhere. For Valve Source games, it's usually <Steam\[yourname]\[game]\[hl2]\save>, but I would recommend googling around for "[gamenamehere] save folder". Otherwise, I recommend a backup tool that copies all your files (preserving folder structure) to another drive and then reinstall.
I seemed to have fixed my crash issue but thank you all for your help, I've backed up my important saves like mass effect etc. REALLY appreciate the kind community here. When I post questions other places I usually get silence, or snarky comments acting as if I don't even know how to plus my power supply in.
Trust me, I've been burned by that.
Copy your saves games to a portable HDD or Dropbox like Scooopex mentioned and paste them back once you're finished installing the games again.
Anyway, the backup took about 18 hours for me for about 60GB of games, which is insane.
And now I lost my Mass Effect 1&2 saves since it doesn't back-up saves.
The Steam backup is the only thing Valve didn't do right in Steam.
Like these guys said, the saves are EVERYWHERE.
All Bioware games for example, are saved under MyDocuments---->BioWare
I think most games are saved either in your "My Documents" folder or "My Documents/My games"
I seemed to have fixed my crash issue but thank you all for your help, I've backed up my important saves like mass effect etc. REALLY appreciate the kind community here. When I post questions other places I usually get silence, or snarky comments acting as if I don't even know how to plus my power supply in.