Ones i tested: Virtual DJ, Mixvibes, Traktor DJ, Traktor Studio, DSS DJ
I tested these as they had the best reputation, and generally the best extras like FX and other stuff.
Traktor range of software seems very easy to use, good beat matching and other auto features, good filter and EQ section. But alas, no FX otherwise. Also studio version suffers from no support for second card, only multiple outs from one card. Traktor DJ on the other hand has amny of the features of the studio version (plus 2 card support - horay), but at a much cheaper cost. Less flash filter/EQ, but still great and has excellent loooping facilities. Very easy to use, beatmixing/looping/filtering tracks within minutes. only about 35euro dowload version. I would recommend this to anyone.
DSS DJ works in a very similar fashion to Traktor DJ, similar filter setup and EQ, and similar looping tools. Adds some effects, but only a few and no 3rd party support except for proprietery plugin SDK. The effects are pretty crap. Traktor beats this on pure easy of use and instant fun value.
Virtual DJ is the next step from atomix (some may have seen ejay mixing product, used the same engine). It has decent looping tools, some FX, but sadly the DirectX plugin support seems sluggish and buggy. It is a fun piece of kit, but for example you need to switch panels to access EQ/FX and other sections, so not very intuitive. Given bugs and interface problems, not worth 99euro i feel.
Mixvibes 5 Pro stands out a mile for me, it has brilliant control over the sound, with extensive looping including reverse looping options. Great built-in FX that cover loads of ground, lfo controlled filtrs, flangers, chorus etc. Also DirectX plugin support, crashed a once or twice on exiting plugin but to be honest the included FX are so useful its not a huge issue. Probably many plugins would work fine, i only tried 2.
Furthermore, Micvibes supports up to 16 decks for truly creative mixing, a very customisable crossfader with 3 band EQ crossfader built-in, global filters, limiter, compressor, EQ, recording, sample-player etc. The list is long..
The Pro version is 109Euro. It really seems to cover everything a creative DJ could want, and in terms of sheer number of features it basically destroys the competition. I've scoured the net and checked many more than i've mentioned here, and this has the best feature set of them all.
Last thing to mention is that in order to have MIDI controller support, you have to buy the Pro EX version, this is another 60euro. Keyboard control in pro version is pretty great however, aside from config file setup, but not a big problem.
Hope someone finds all this crap useful