The best and most realistic drum software (without spending big money on Halion or Giga Studio) is either DFHS (Drumkit From Hell Superior) or EZdrummer - both by Toontrack. Check them out - they both have a humanizing feature which automatically changes velocity and timing and draws the sounds from a huge library of real drum samples so it sounds very natural. DFHS also has a masive ammount of options such as mic placement and type and levels of bleed. You can also buy a huge library of pre-programmed midi beats specifically set up for DFHS from Groove Monkey - you can copy, paste and splice them together to create just about any beat you can imagine.
Either that or mic up a real drummer in a cheap studio on a cheap kit, then track each of the drums separately (everything needs to be mic'd separately - including all cymbals) - then use something like Beat Detective to allign each hit for perfect timing and remove all unwanted mic bleeding. You can then use a refill-style software such as Drumagog to replace all of the badly recorded drums with expertly mixed and engineered samples. It's a lot of hassle but the end result is a true professional sound, this method is widely used in pro-studios and you have more than liekly heard it on a few cd's in your collection (it can be used for either just one drum or an entire kit). If this sounds like too much work then check out DFHS or EZdrummer! Battery is also a cool program worth having a look at.