Here are some I've heard of in the past:
http://360idev.com/
http://cocoaconf.com/home/announcement - sadly already done for this year
Looks like those are the only ones left that are more
developer-centered. I remember there was another one, but I think it
shut down a few years ago.
-warner
WWDC's biggest benefit is that you get access to Apple's staff and
they can help you work through hard problems. It's also simply the
biggest Apple dev conference out there, hence the most chances to
interact with other people. As it's pretty obvious that Apple is
likely to rev iOS (and now OS X) on a yearly cycle, WWDC is mostly
going to be about changes to the OS, new API's, etc. It's a 5 day
firehose of information, which can be a bit overwhelming.
The only other conference I've been to is the MacTech Conference which
is dual track Ops/Dev with about a 70/30 attendance split. The dev
sessions I sat in on were quite good, being done by people in the
industry, not with the extreme polish WWDC preso's get.
If you're shopping around, I'd look for schedules and preferably video
or speakers preso decks from previous years conferences, and then use
that as a way to forecast what you're going to get out of it.
- Zack