02-03 cheapest wrx's you can find. people say they have a weaker tranny, I drove mine to 195k with no issues before someone ran into me. If you want the heart and soul of a wrx, cheap awd turbo get one of these.
personal fav: 2004 STi, because the center diff can go into rear wheel drive with a few clicks of the parking brake.
2006 and 2007 wrxs. get the 2.5l engine, which is a pretty big deal and probably the most notable improvement over the first 6 years of wrx.
2008+ :