Do you mean "composition" as in weight of the image, balancing the areas around the entire frame by color, brightness, etc., and leading the eye throughout, or "compositing" meaning how to integrate a bunch of different elements into a single cohesive image (I'm guessing the 2nd, but it's an entirely different answer than if you were looking for the 1st)?

Composition - just off the bat I'd suggest getting copies of ImagineFX magazine at your newsstand. Fantastic articles and tuts throughout! This is more of a "art" question, of which there are TONS of books on composition dealing with black&white or color, weighting and balance of the frame - rules of triangles, thirds, spirals, etc. How to find you focal point, how to lead your viewer through the image, etc.

Compositing - several books come to mind - but "I Have a Human in My Throat" by the guys at worth1000.com (you'll LOVE the cover - and check out the site!) is probably the fastest and most thorough ticket for you to dive into bizarre compositing techniques. There's plenty of others, but once you learn the heavy tricks, the rest of the books start to become "yeah, I can already do that..." and it comes down to little tweaks here and there that you learn.

If you haven't already, seriously consider becoming a member at www.photoshopuser.com - it's $100 per year, you get the magazine subscription, discounts at a TON of places (B&H, Calumet, Graphic Authority, etc.), discounts to seminars they hold all around the year, and access to a seemingly unending tutorials gallery.

Hope this helps-
-Lew ;-)