TBL for sine & then lots of lovely plugins. 3xOsc that ships with FLStudio's also pretty potent and flexible provided you know how to get it going right - even just using the randomize feature can elicit some pretty good initial settings (which you can then phatten with FX) - I know of several fairly popular producers who use 3xOsc, and their stuff sounds leet.
Reaktor (the Menace, Carbon, and Dragon ensembles in particular) - infinitely versatile
Z3ta - 6 oscillators, loads of nice waveforms, mod matrix
Minimonster - prolly the best software filter I've heard, the morphing/mutating feature, excellent presets
Godkiller III - a freebie but pretty cool