On pentax, it's M42, bit's 'n bobs of jiggery pokery with nikon F and perhaps OM or CY (tho' the latter 2 will require a little destructive modding, or replacing, of the bayonets) - and that's it!
If you really want to play around with the range of vintage lenses, get a mirrorless eg Nex/Alpha, Lumix, Olympus, samsung...
FYI:
http://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html
Cameras can (in principle) mount lenses from a system with a
longer registration distance and keep infinity focus. That's why canon is the most adaptable dslr - see
>adapters mounts and tubes on ebay. All those mirrorless have short RD and so there are simple adapters for most mounts.
Adapters that overcome the registration distance issue by including optical elements are a lot more expensive and generally not recommended.