Instrumental music, eh? Well, you already know that I have taken a liking to [I]Two Steps From Hell[/I] and [I]audiomachine[/I], both of which being sources that have served as sources of musical themes for my characters in the past, and the composer Michael Riske also strikes me as quite good, though not as productive. Other nice sources of music readily available on YouTube would be [I]Brand X Music[/I] and [I]Immediate Music[/I], and also [I]Ethos Music[/I], though I haven't heard enough from the latter to confirm the general quality. And games with aggressive, powerful music... Well, the original Halo had some great music in it (every couple of years I like to replay it just for the music), which has been redone in countless different versions over time. In terms of powerful music, the soundtrack from Final Fantasy VII: Crisis Core has some pretty notable examples, I think...
That's all I can think of right now, I think. Will mention it if I think of any more.