Few points:
1) The SSD won't make much difference aside from the LOAD times. As long as you realize that.
2) The Samsung 840 EVO is the best choice IMO. It also comes with Samsung Magician software that easily allows upgrading the firmware etc.
3) You need to OVERPROVISION the SSD (Samsung Magician can do that). You'll have at most 95GB left.
4) ?? All4Me is mentioning a USB Flash Drive. Ignore that. You don't run games from flash drives. They wear out quicker and don't have the same wear leveling correction. I'm surprised someone even recommended that.
Even if they were, the ones listed here are no-name brands with about 9-22MB/second read speeds which are way, way below SSD speeds (The EVO is up to 550MB/second or so). They also cost $60 for a 128GB model and you can get a good SSD for about $90. Makes no sense at all.
5) As said, you need to UNINSTALL, then REINSTALL the game while manually choosing the location (the SSD). That's probably going to take a while, especially if there's a lot of updates that need to be downloaded. Your GAME SAVES should be all online though.
6) STEAM GAMES:
You can create a 2nd Steam folder for games that do benefit from fast load times (any game like Skyrim with frequent loads due to map points, or entering buildings etc).
In STEAM, you can move games between folders (BACKUP, Delete Local Content, then RESTORE but choose the 2nd Steam folder on the SSD).
*You may wish to get a 250GB Samsung 840 EVO instead if you have a few more games you'd like to add from Steam or other that would benefit. In that case, I'd make two folders:
a) E:\Games, and
b) E:\Steam2
Install WOW into the first one.
**After overprovisioning which leaves roughly 92GB of usable space, you'll have about 61GB left after WOW. Most games use closer to 10GB though so you might have room for several more games. Again, just for ones that need it. STEAM is so easy to MOVE games so you can just have the ones on the SSD that you're currently playing.