Canon EF 35-80 with the front chopped off. Here's two I handheld last night.
First is at 35mm F/6.3, second at 80mm F/13. Unsharpened/processed, but both lost a bit from the resizing and compression.
It goes from ~.9x life size to well beyond. Figure that last frame is a 1.3cm wide pop tab on a 3.6cm wide sensor. Goes for ~20$ on ebay everyday.
I have a 35-80mm Canon lens that I removed the front lens element as well. it's all manual since Autofocus will work...but without a front element won't lock on focus. Bought it off eBay for around $20. great little lens to play around with.
about as cheap as you can get for a manual focus macro. 


