I'd second the vote for Stylus RMX for 2 reasons.
1 - they released a new version called RMX Xpanded, which includes 5 discs of additional content (for a 30 gig library)
2 - The new Spectrasonics synth Omnisphere looks like it'll be the next big thing, and the arpeggiator in Omni integrates with Stylus RMX, so you can very easily add synthesised pitch elements to your drum loops that lock perfectly into the groove.
If you get RMX now, that'll cover the drums, then when Omnisphere comes out, that'll cover your pads.
Having said that Massive is great for rhythmic textures, and it's pretty simple to program rhythmic patterns and assign them to various parameters.
You could also have a look at Camel Audio plugins, Camelspace and Camelphat. These are effects that can be used to radically alter your existing library of sounds. I use them all the time, easy to program and amazing sound, perfect for anything trance. I know BT uses them.