Sure have! Mostly M42 stuff. Can be a bit trickier to get the full Helios swirly effect on a crop sensor but you can still get some nice results
I'm a big fan of SMC Takumars — render stuff beautifully, handle silkily and are built like tanks. Have a bunch of Russian stuff (Helios 44-2, Mir 1b, Mir 20M, Jupiter 11A) which all give quite interesting looks. If you can find a 1b cheap then it's a fun one to play around with by reversing the front element.
Managed to find a Minolta MD 35-70mm macro a while back for around £15 (It's a Leica design/Minolta build but the Leica-branded version usually goes for £400-600). Fantastic Minolta colours, great bokeh. Not the fastest lens, but it's one of those zooms that's like a pocketful of nice primes.