Thought this was worth more than a tweet – Microsoft Research Labs at Cambridge are offering 12 week internships for PhDs. (They will very occasionally consider super-talented UGs and Masters but prefer candidates with 2 or 3 years experience at PhD level.)
They take applications all year round, but if you want a summer internship, you should get your application in now. Their website says “before March” but an ad currently posted on Monster says 21st Feb. I’d get in well before either of these dates if you’re interested. Internships are paid, with some help towards accommodation and other travel costs.
In addition to a CV, you’ll need to write a Personal Research Statement, which is a critical part of the selection process. Even more importantly, you’ll need to get your supervisor, and potentially your PhD funder, on board before considering this opportunity – there may be restrictions from your funder, and your supervisor may have other ideas of what you should be doing with your time (like getting some results…) However, this is just another of those heaven-sent opportunities to develop your negotiation skills.