It's in London, so I know it will only be of interest to a minority of HN users, but the Mozilla Festival takes place at the end of this month:

http://mozillafestival.org/

It promises to be a fantastic conference. They have a couple of interesting talk tracks like "Look Who's Watching" on surveillance on the internet, as well as more traditional tech topics.

Even better, tickets are only £40 (£3 for under 18s) and it takes place over a weekend. So it should be accessible to nearly everyone.