If you want to search for other solutions, the keywords 'aero snap' might help you. This is how it's called in Windows 7 and many users and developers try to copy it from there.
I used the following two solutions, but I haven't tested them yet on 11.10 and I didn't test the third one at all. The biggest disadvage with all solutions I've found so far: there is no easy way to get the windows back to their original size and position.
You'll need the package
compiz-fusion-plugins-extra. Install it using the package manager or using the following command:
sudo apt-get install compiz-fusion-plugins-extra
Then open the CompizConfig Settings Manager and search for grid and enable this plugin. You can then place the active window to the left half
Compiz commands allow you to define custom commands executed based on specific bindings such as moving a window to an edge of the screen. Detailed instructions are available here.
gTile in Gnome 3
Use this gnome 3 gTile extension to resize and place your windows on a grid. This extension was inspired by Divvy for Mac OS, so you can watch this video to get an idea of how it's working.