I use a thing called Carbonite. It is the same company that gave us winzip so is very trusted. My bro in law is a programmer and swears by it. You pay around $40-50 a year (which is about £25-30, look out for deals on the web). The great thing about it is that it runs quietly in the background and when you ammend anything at all on your comp it automatically updates it on the server. Even if you change the directory of a file it will do this. Also just say you by mistake (and this happened to me, but thank God I had Carbonite by then) you copy over a file or save it with the wrong name and write over another word doc (as you can easily do when you have so many with similar names, eg. Methodology v1, v2 etc), it will give you the option of downloading recently backed up versions.
Basically it is great. If you don't mind spending the money I would get it. I wouldn't usually spen the cash, but I just thought, if I lose all of my hard work I will be royally screwed!
Oh and also it is unlimited! My bro in law has all of his songs and movies backed up, around 55GB!