I'd pretend someone named "Bartholomew SSD-Owner" asked this, but that didn't happen—I'm just certain it's been asked, and I wanted to bring a program called SteamTool Library Manager 1.1 to your attention.
It was more useful back before you could set alternate Steam install directories, but if you run a small SSD and only want whatever you're currently playing on it, SteamTool makes it easy to shuttle games to and from your storage disk. Sure, you could just find the game's folder and move it to a second Steam install folder on your HDD, but that'd take like, precious extra seconds.
Generally, this got me thinking about all the ways we customize Steam or use external tools to make it better. A while back we shared some of our favorite Steam skins, but here's some more useful Steam-related stuff. And because I've inevitably left out your favorite, share it in the comments!
steam.tools — A much better way to browse the Steam market for trading cards, backgrounds, and emoticons.
Depressurizer — Helps organize your library, and can auto-categorize games using data from their store pages.
SteamPrices— I use this site, among others, all the time to track discounts.
SteamDB— Another great way to track what's going on in the Steam store.
Steam Left— Estimates how long it'll take to beat your backlog (more frightening than useful).
Steam Charts — Find out what people are playing.