For DJing, a mixer is pretty much a must, a lot better for such a setup and should work well with a PC as a sound card.
I use a Steinberg UR22 MkII for a typical PC-based setup (MIDI controller, headphones, speakers, you know the drill; might post in the setup thread one day). It does just what it's supposed to (2 inputs, 2 outputs, rock solid without noise, records superbly and the drivers work very well) and is a rugged little thing (metal body, weighs about a kilo).
It's pretty much identical to the more well-known Focusrite Scarlett 2i2 at the same price point, but offers more features like a MIDI input and output, better build quality, a knob for the loopback to monitor volume ratio and the option to run it off an independent power supply that it doesn't come with.
Meanwhile, the main pull to the Focusrite is that it looks slicker and has the phantom power toggle on the front (IMO way more convenient than the UR). I've heard that their preamps give a bit of a different colour to the sound, but haven't had a chance to test that out.
If I could recommend anything regarding buying audio interfaces, don't settle for less than a UR22, 2i2 or equivalent - you're going to get worse sound out of the cheaper interfaces that only offer unbalanced output and are generally lower in quality - I can speak from experience of buying a Scarlett Solo out of pure ignorance and getting disappointed.