In a long, thoughtful and informative post, Charlie Stross explains why he'll be voting LibDem in tomorrow's elections. So will I, for largely the same reasons. I was thinking of writing up something that explained why from top to bottom, but Charlie's really nailed it.
I will add this: of the three front-running parties, the LibDems are the only ones that don't believe that I, as an immigrant, should be forced to carry biometric, radio-enabled identity papers. And they're the party that has an official policy of internet freedom and balanced copyright.
If I wasn't voting LibDem, I'd consider the Greens, who, I think, are great on everything except homeopathy (I also have some quibbles with the LibDems, for what it's worth -- but they're minor compared to the large policy questions.)
They appear to be more flexible and pragmatic, and much more deeply committed to civil liberties and decentralization and reform of political power than the other major parties. They're committed to abolishing the National Identity Register (which alone would be enough to capture my vote for an election), and more importantly, their party framework is based on a value system I understand.
I've also met my local LibDem candidate, Dave Raval, and believe him to be principled, committed, and intelligent, and would be proud to have him represent me in Parliament.
Likewise for our neighbours in Islington, whose LibDem candidate, Bridget Fox, deserves the bottomless thanks of every geek in Britain for sticking her neck out to get the party to adopt its forward-looking stance on copyright and the net. Bridget, a former librarian, has the makings of a hero of the information age, and would be an outstanding MP.
Update: Before you ask, yes, I get to vote here, though I'm not a citizen. Privilege of the commonwealth -- Canadians, Indians, and other commonwealthers legally resident in the UK get to vote.