i have been using a mix of program for a wile and well found nothing 2 wright home about so i recommend spending sum cash and going for a hardware option something that will put really dj controls at your hands but still run from your mac i recommend for a beginner/new to mp3/laptop dj'ing something like this Behringer B-Control Deejay BCD3000 with Traktor 3 LE DJ Software look on a dj supply site for your area
LOL says who? Rane Serato Scratch Live was just voted the top DJ software(nonproduction) by DJ Mag, who also runs the 'dj of the year' which is a very very very large pole. The new Traktor scratch is better on paper, but the software interface is cluttered, and there is not as much support. Rane admits their software will not crash if you have a proper computer and no corrupted music. Thats why I chose it.Traktor is the one to go for tho as thats what the majority of professional mix dj's use when creating mixtapes.
^^ I'd listen to these guys...especially david, seems to know what he's talking about