Scratch Live is a beautiful thang (to misquote Spike Lee). Apart from the convenience of carrying around thousands of tunes in a laptop rather than lugging record boxes (and having doubles of every tune, and being able to treat any digital recording as if it were vinyl), you are also able to sort by BPM and quickly find tracks on a similar tempo - which gives rise to some combinations you might not otherwise think of.
This does mean, however, that you have to go through the laborious task of checking and saving the BPM of each of your tracks. There are some programs out there that claim to be able to do this automatically and in bulk, but don’t trust em. Maybe it works for house or techno, but if you’re playing proper music with a breakbeat or a broken beat or a one drop or a two step - or anything but the dumb rigid beat known popularly known as “4/4″ (technically, pretty much everything mixable is 4/4, even the most hectic out-there drumfunk, but that’s beside the point) - you’re stuffed.
So you have to do it the hard way, tapping out the beat while you listen to the tune on some kind of BPM counter. I used to use this one, but it’s buggy as, and I don’t think it works on Intel. I just found out about ltjBPM (nothing to do with Bukem, as far as I can tell). It works much better, you use the keyboard instead of the mouse, and it has a chimpanzee as the icon. What more could you want. Well done that monkey.