You should also delete all system restore points except the most recent one. This can be a real space hogger, but not knowing your OS it is pointless trying to tell you how to do it.
Videos are probably the biggest space hog - have you downloaded lot of movies?
There is an excellent free program that scans your hard drive and shows you in easy to understand which are your biggest files.
http://www.disksorter.com/
Only ever delete files and programs that you definitely know you do not need or want. Deleting files willy nilly can seriously boooga up your pc