... Edinburgh, Imperial College, or perhaps Manchester (they have one of the earliest electronic computer, still in working order). There's also Canada -- Waterloo has a renowned engineering program.
Not sure if Cambridge does exchange programs, but if you're abroad for a year instead of a semester, their Part II CS tripos is quite gruelling; it's basically a complete undergrad education done in one year, usually taken by people who already have a degree in related fields (e.g. math or physics).
In the UK, my rule of thumb is: if they teach a functional language then they are decent. Edinburgh is where Standard ML was written (and Phil Wadler is in the faculty) -- oh, and is really good for Artificial Intelligence research too, so naturally, they're quite heavily into Prolog too. Cambridge also uses ML; York uses Scheme and Haskell. Warwick -- ML, I guess.
There's also the location to consider. Imperial is in London -- good place to be, but accomodation might be tough. Edinburgh is in, well, Edinburgh -- lovely place, a bit cold in winter, but not as bad as the northern parts of the US. York is on the east coast line, so it's less than three hours from either London or Edinburgh by fast train. Warwick, despite the name, is not in the quaint mediaeval town of Warwick, but in nearby Coventry (they obviously thought naming it the University of Coventry would not be good for business). Not far from London and Birmingham, though.