There's practically an adapter to mount any lens to any camera these days, and here YouTube member videotestground talks about the Pentax M42 Super Takumar 50mm F/1.4 [Thanks Vedran]. These M42 lenses are older manual lenses for Pentax film cameras that can be mounted to your Canon DSLR through a cheap adapter. A Canon 50mm F/1.4 will run you close to $400 dollars, so you could save quite a bit adapting older manual film lenses. He also goes into showing a small step up filter adapter, and examples with a static ND filter to shoot at the wide aperture in the bright day.
You can find these old lenses for your Canon DSLR on eBay (click here).
Pentax Asahi Super Takumar 50mm F1/.4
And you can find the adapters needed to mount M42 lenses to Canon cameras (click here)
M42 to Canon EOS Lens Adapters