The big question is how much do you want to spend? On the cheaper end, I'd point you to Adobe Premiere (
http://www.adobe.com/products/premiere/ ). It's a very powerful software package that integrates well with the other Adobe products (After Effects, Photoshop, etc.). If you want to go more upscale there's always the Avid Media Composer (
http://www.avid.com/products/Media-Composer-Software/index.asp ). This is a professional level editor used by the majority of Film & Television production companies in LA. Avid retails for around $2500 but if you have a student ID (or know someone who does) you can pick it up for under $400.
Hope this helps,
Michael