Unpaid time off is fine. You'd be surprised how few employers are willing to accommodate that. My current employer is a tight knit software firm, so it's not such a big deal if I take long unpaid leave at the end of a major project or milestone. I have a skill set and background that's difficult to train up.

Edit: I should add that this may be an unreasonable expectation but it's the expectation I need to have in order to be stably employed.