I've enjoyed using a Kelty Dart II, which is a bivy-style, single layer, one-person tent. Very light and can be had for around $120-150 U.S. There are also other similar models (some of which I suspect are better than mine), like the Shires TarpTent, the Mountain Hardwear Bivy (both mentioned above), the REI Roadster, the MSR Zoid, and the Sierra Designs Clip Flashlight CD.

Some pics of me and my tent: