I've been asking myself this question. I'm fortunate that I get to go to one conference per year. But which one?
There are several options. Not least of which is the Code4Lib 2009 Conference (registration opened today).
In case your wondering: I've chosen Balisage: The Markup Conference. I've accepted the fact that I'm turning into an XML/XQuery geek :)
Any thoughts on other good conferences?