I went to Colchester Sixth Form college, and that was really good. It's not so wonderful for computing: people doing A-Levels have to code in Visual Basic. People doing IB (the International Baccalaureate diploma: Basically A-Levels but you do 6 subjects) have a choice though. For my year you had to do it in Java, but now you have a choice. The college (like I said, with the exception of having to code in VB if you're doing A-Levels) is really good.
Just looked it up and it seems very good. I will probably do the IB if I end up going there.