One place to start is the Times Higher Education league table, divided into 'Top World Universities' or by broad subjects, such as Engineering and IT, Life Sciences and Biomedicine, Natural Sciences, Social Sciences and Arts and Humanities.
US News has also got quite an easy grid system to get your head round, again dividing its list up into subjects, but also methodologies (so, student-faculty ratio, research etc...) as well as location (in terms of continents).
You have to bear in mind, though, that QS seems to be the big daddy in terms of world university rankings, with the Academic Ranking of World Universities hot on its tail (no pun intended).
It's also quite difficult to judge some of the establishments out there, due to the fact not all tests and surveys run by the QS/ARWU assessment are relevant to, say, History of Art courses, for example. A good bit of noseying about the internet, emailing some course coordinators and thinking on your feet will get you somewhere, somewhere good. Most South American and African universities, for example, are hardly mentioned, if mentioned at all. We could wax lyrical here about what universities you should go to, but it all depends on where you want to study, what you want to study and how much you're willing to put up with. Students in different countries act differently, courses are not structured the same as in the UK, and you might actually find that in some instances WORK and lots of it is required from foreign lands. The famed French Grandes Ecoles, for example, are notorious for their hard-nosed attitude to exams, huge amounts of work and stressy students. However, you'll reap the benefits - the results and high standard offered is second to none. Did we mention the entrance exam? Best to get those books cracked open pronto. 
Of course, some establishments choose to opt out of the world rankings selection, for reasons that vary from the elitist viewpoint (a kind of 'we judge ourselves by the kind of students who apply' mantra), politics (disagreeing with the surveying system) or because the standards offered at said institution may not be what QS or ARWU deem to be the best. This is not to say they are not worth having a look at. Your best bet, regardless of what you are reading at university, be it the Arts, Social Sciences or Computer Science, is to focus on the top dogs in the business. That is to say, your favourite geek of the subject - Albert Einstein studied at the Polytechinc Institute in Zurich, Roland Barthes at the Sorbonne, Stephen Hawking at Oxford... Pick your celebrity know-it-all(s) and get checking the course requirements from each establishment you come by. If it was good enough for them... 
