I just added support for Quake 2 levels this week, but I've also added support for GoldSrc as well, so Half Life and Counter Strike maps will also load.
For some test levels, I would go to slipseer.com and download some of the community map jams. There are hundreds of maps to play with and many of them are really great looking. You could also buy the Quake Rerelease on steam pretty cheap.
