I was looking at Pentax listing on Craigslist last week (bad thing to do, really) and I stumbled across a listing for a used A 135mm F2.8. I've always been interested in picking up a manual focus 135mm and like the flexibility of having auto aperture on an MF lens.
Long story short, I landed a nice, clean copy for an even nicer price ($95) and find it's a good balance between reach and size. Great for a walkabout lens even with a minimum focusing distance of 1.2 meters. Good contrast depending on angle of light and sharp (when the shooter can get the focus right...), and pleasant bokeh. Only thing I noticed is that after taking a shot, there's a slight mechanical sound (hope it's not problematic!).
Some sample shots: