i would strongly recommend Serato Scratch / Tracktor Scratch. I'm not that keen on CDJ's. I mean, the technology is awesome, but for me, Technics still (after 10 years of me using them) come through. I enjoy mixing on them and i think my mixing is better on them, CDJ's for me are a tad too sensitive for me, and i just dont like the feel compared to Turntables. Also with Serato you can flick the input switch to play "normal vinyl" and flick it back over to Line to play mp3's through the timecoded vinyl.
Serato allows for the turntable feel whilst playing the latest MP3s. Making doubles is a doddle on Serato too.
TECHNICS TECHNICS TECHNICS people!
As an aside, i feel that CDJ's are killing dance music. The very grass roots of dance music have been taken away...White labels! With CDJ's (and the ability to literally burn and play the day you made it) it's now all about people making their own mashups, thus oversaturated the market with them. Its pretty obvious the quality of dance music was better 8 years ago compared to today, and the absence of vinyl is no coincidence in this factor. I could go on, but this is just what i feel.