What is the best branching strategy to use when you want to do continuous integration?
I've recently come to like this model when using git. Although your question is tagged "svn", you might still be able to make some use of it.
Continuous Integration can to some extent happen in the "develop" branch (or whatever you call it) in this model, though having long running feature branches for future releases wouldn't make it so rigid as to consider every change happening to code somewhere. The question remains, whether you'd really want that. Martin Fowler does.