What are some good Metroid-like games?
 

By "Metroid-like" I mean platformer games where as you play, you see items or areas that you can't get to because you don't have the necessary weapon or ability yet. Then you get to a room or beat a boss that gives you something that then lets you go back and access that area or get that item. For example, a double-jump upgrade that lets you get up to higher platforms that you couldn't reach before.

I've always loved that game mechanic, but it seems like it's never used. The only other game outside of the Metroid series that I've seen use it is Shadow Complex for XBox Live. I've heard people say Castlevania: Symphony of the Night is similar, but I don't know where I can get my hands on it. With all of the games being released for PSN, Xbox live, and Steam, I'm hoping there are some out there that I've missed.

I was going to suggest Shadow Complex and Castlevania SOTN. Both are available on xbox live -- well shadow complex is a xbox live exclusive. Both of these games are fantastic.
I assume you've already played Shadow Complex?

Yeah, I played Shadow Complex a couple of years ago and loved every minute of it.

I didn't realize SOTN was on XBox live. I'll definitely check it out, thanks!