the s2 is awesome. I mean it's my first controller but I'm pretty confident you can do everything possible with 2 decks on it. 2 two sample decks really make it into a 4 deck controller anyway. I'm at the point where I'd be pretty confident playing a club or show on my s2. Looks like it's $560 now, I got really lucky and got it for $300 on a crazy amazon sale.
The Traktor pro 2 is great software as well. The only other DJ software I've tried is virtualDJ, and it blows compared to Traktor. The coolest thing I've found so far is the grid on the tracks. For instance, say I want to mix a 70bpm reggae song into a 140bpm dubstep track. You can just multiply the reggae song's grid x2, to make its BPM 140 (without speeding up the song). Alternately, you could divide the dubstep song's grid by 2, making its BPM 70. Shit is so cash.