I would recommend Traktor Dj Studio software.

Traktor DJ Studio stretches the limits of conventional tools by opening up a whole new world of real-time sound-alteration possibilities. Spot-on beat matching with one click, up to 10 tempo-precise loops and cue points, a well-equipped DJ mixer, a powerful database, complete remote control, mix recording, overdubbing, and fast mix exporting are only a few highlights from Traktor DJ Studio's extensive list of features.

Present your own DJ style live on stage and record the mix to disk. Interactive wave displays, superb EQs, one touch loops, automatic beat matching, and scratch presets are the secrets of Tractor DJ--the perfect fun machine. The application's features include an MP3, WAV, and audio-CD player with two decks and professional sound quality, as well as fully automated tempo and beat matching, beat-sync display, pitch control, and fast-seek mode. There is a crossfader for manual mixing and an autofade function with adjustable time, punch-in, and boost buttons. The program also features a waveform display for visual control, for stopping, locating, and scratching the music track. Tempo-synced loops can be set on the fly, moving and resizing during playback.

You can download it from here.
License Free to try; $199.00 to buy

The best free dj mixer software is Tactile 12000

Tactile12000 is a QuickTime-based, 3D simulation of a DJ setup consisting of two virtual turntables and a mixer. It allows you to crossfade, backspin, speed up, and slow down music, including full-length WAV and MP3 files, on your computer. You can mix the songs, or it can automatically crossfade between the songs stored in your MP3 playlist.

Version 2.1 is now free and open source. The Mac version contains bug fixes and minor enhancements that are described further in the release notes.

You can download it free from here.