Nothing beats WWDC's access to Apple engineers, and the confluence of global (well, provided you were awake in time in certain parts of the globe) attendees. If you didn't get a ticket to WWDC, however, there are still plenty of other great developer conferences for Mac and iOS developers. Here are just a few, but feel free to share more in the comments.
MacTech Conference - There's a developer track here, although MacTech's forte has always been IT. They put on a fantastic event, however, with great sessions, after-hours events that are not to be missed, and camaraderie in spades. Plus, there's a series of IT-focused events around the country now. (Full disclosure: TUAW is a media partner with MacTech.)
360MacDev and 360iDev - Held in Denver, both 360 conferences are developer-specific and crammed with useful sessions led by renowned developers from around the world. I've been to a 360 conference, and I can tell you that what you'll learn after hours is almost as good as what you learn in the sessions. Sometimes a conference benefits from being smaller and more focused. (TUAW is also a media partner with the 360 folks.)
Voices That Matter - Pearson Education has put on the VTM conferences, covering web development, iOS and Android among other topics. There's nothing on the 2012 schedule at the moment, but keep an eye on their site.
SXSW Interactive - OK, this is the least focused of all, but there are usually good lessons to be learned here from seasoned developers, not to mention business people and other industry wonks. Of course, the after hours meetups and interactions are priceless. This is one you can unconference with great results.
Game Developer Conference - This is a game-focused conference for developers and publishers, and has become a great place to meet and learn if you're in the game business. It's not Apple-specific, but is a great place to meet developers and others who can help you build amazing games.
Unite - The explosive growth of the game platform Unity has made their conference a must-attend if you use Unity to make games on iOS. Of course, Unity is a cross-platform tool as well, so expect to rub elbows with web and "other" OS devs as well.
Appsterdam - Not a conference itself, but the European developer collective is a rallying point for a number of meetups and other events in Amsterdam and elsewhere in the EU.
There's also the option of going to San Francisco during WWDC without tickets -- but I'd only recommend that if you have friends who are going.
CocoaConf - "CocoaConf is a focused two day, three track conference for iOS and OS X developers, with an optional pre-conference iOS tutorial."
One More Thing Conference - "One More Thing isn't a traditional programming conference. It's a meeting for iOS developers, designers and those who just want to come along for the ride."