My favorite sleeper is the KA mount Tokina 90/2.5 Macro. It's extremely sharp wide open, goes 1:2 by itself and 1:1 with matching adapter, it's compact (sans the adapter, but I don't need it often), the focus ring turns Pentax style, and the bokeh gives it its "bokina" name.
It's still fairly cheap $300-$400 range.
Another deep sleeper is the KA Spiratone/Soligor 20/2.8. It's compact for a 2.8, nice sharpness stopped down, and it's bokeh is psychadelic (some think in a bad way, I think it's great). It's an odd duckling, so it'll never be popular, but I like its character.