Complexity of Light by Children of Nova and Africa by Quartered are probably my two favorite RBN tracks on drums so far. Both start with great solos (the Africa one is so long the demo ends about 60% of the way through it), and then go into a wide variety of fairly technical and unique patterns after that.
If you're looking for an insane, mayhem level challenge, go with Mordecai, Pack Flier, or Day of Mourning. Mordecai's actually fairly fun and relaxing for the last four minutes if you can get through the beginning or play with no fail mode, but unless you're amazing at drums you also might just fail every time at 2%.
Makeup/Breakup is good if you want something challenging but not metal and without blast beats. It's got one of the most confusing, technical drum charts in the game, but can be pretty fun if you can figure it out. Trippolette is also good for something very technical but slightly less difficult (at one point it has your hands playing in 7/8 while your foot plays in 6/8).
Other recommendations include Footloose and Fancy Free, Battles and Brotherhood, everything by Fake Shark-Real Zombie!, the Ultra Saturday songs, Genius, Bleeder, the Speck songs, the You Shriek Songs, Rx, and Demon Woman. Also, I haven't actually gotten it yet, but Destructive Device seems like it might also be a good one.
There's probably some other good songs that I'm forgetting, but that should get you started. A bunch of those songs are only 80 MSP, too.