The one app I've been really happy with so far on my Android Tab is Unified Remote.
It's a great media center remote, it has the basics like touch pad/mouse and keyboard but also comes with remotes for Windows Media Center, Youtube, VLC and you can access start menu, task manager and a file browser. All of this is available ad free on the free version, apparently the full version has voice control and a few other remotes but the free version has just about everything I need.
The one thing it could use is the ability to see your playlists and songs in WMP so you can fire up an album without needing a screen on to see what you were doing.
All you do is download the app and then get the server software from the website and install that on the PC you want to control.http://www.unifiedremote.com/