Internationally, Manchester, some London colleges (University College London and Kings College London being the most obvious), the London School of Economics, Imperial College London (simply because London is an international city, I'm guessing that having "London" in the name will act as a brand name). St. Andrews because it's where that posh bloke that had the wedding went.
The Russell Group unis are generally quite respected:
http://www.russellgroup.ac.uk/our-universities.aspxI'd say Warwick, Birmingham, Edinburgh and Leeds would be the most recognisable to a foreigner. Maybe Glasgow because of the size of the city. Maybe Sheffield. I'm unsure about Warwick as it is relatively young on one hand, but on the other hand it includes the Chairman of Tata Motors, presidents and vice-presidents of various countries and the managing director of the world bank among its alumni.
Certainly any of the above are respected in the UK, no matter what the nerds on TSR tell you (compensating for small penises I'm sure). There are plenty of good institutions that aren't so recognised on the world stage, such as Durham, York, Bath, Leicester, Lancaster etc. For brand names (internationally) I'd say one of the above London colleges or universities, Manchester or a uni of a big city like Edinburgh, Birmingham, Leeds etc.