Peruse your Steam library for games you haven't played. That's how I found Don't Starve after a friend gifted it to me, and I've been hooked. Going on 7 episodes on my channel so far.
Humble Bundle always has a sale: you can get some good games for literally $1, and they have a pretty good selection of both in-bundle and out-of-bundle games. I'd suggest you check there.
When it comes to playing and commentating, it really depends on you. What type of game do you want to play? What experiences do you want to share? Those questions are the foundation to the type of commentator and Let's Player you'll be, and I think that to some degree, everyone who does gameplay videos has to answer those questions in some way, despite your experience or lack therof.
In short: do what you wanna do. Look on Steam, Humble Bundle, and other sites for inspiration for games you might like to play. I will say that the indie scene is booming, especially on twitter. In the end, people will watch your videos for you as much as for the gameplay, sometimes even more. So always be genuine and true to yourself.
![Smile :) :)](/styles/default/xenforo/smilies/smile.png)