I am going to be getting a new computer with SSD next week and want to be able to effectively preload my games (i.e. not have to start over or transfer save data manually). As I understand it, I want the game files to be on the SSD and the game saves on a HD. I have an external HD. Is backing up my games (via the Steam backup command) the correct thing to do? Thanks so much.
I'd advise you to stay away from third-party software, and instead use the backup feature Steam has. Less hassle, great compression, and easy to reinstall.
Make sure that when you backup multiple games at once, you group the ones that go to your HDD and the ones that go to your SSD together. You can selectively restore single games in backups, but you can't selectively change the install location.
This is the software that i use. It will allow you to make a new folder for steam that can be linked to your standard folder.
This is the method that i would personally use and have used in the past.
Although it can be done by copying files but i have found that some games just don't like that and end up not working.
Razer Game Booster will back up your saved games to a cloud storage service (I linked my dropbox account).
Check here for the list of supported games: http://www.razerzone.com/gamebooster#supportedgames
If you don't want to download all of the games again, you will still need to follow the steps that NoneOfYourBusiness referred to.
I strongly advise to stay the hell away from Steam's backup feature. It usually does more harm than good.
I suggest manually copying the game folders (and saves, should they be stored somewhere else) of the games you want to quickly restore to your backup location and then to the SSD.
When you do that, delete the .exe file that starts the game, otherwise Steam will be unable to detect previously downloaded content. That .exe file will be the only thing you have to redownload, per game.