The Topcon 58/1.8 Auto-Topcor is a pretty terrific lens, and I think a little underappreciated because of being an orphan mount. The Topcon bodies are fun and bulletproof, too---the two make a very good casual knock-around 35mm SLR outfit.
Edit: OK, so that's a little hard to defend as "reasonably light". But still, it's so much fun!
Topcon and Miranda are two I'd forgotten. I'll check both out.