If you live in a big city, just watch the trash, especially come spring cleaning. I generally find what I'm looking for in about a month. I've found about 5 bikes so far. Craigslist.org is another good dumping ground. As for types of frames, go for a 70's or 80's steel roadbike, fugi, shogun, univega, pugeot etc. Just pick it up, if its light enough for you then you should be golden.