It’s so late in the year, we almost forgot that Facebook hadn’t held its annual F8 developer conference yet. Today, the company announced that it will take place on September 22.

Facebook says the event will be spent exploring topics including:

• New Products: We have some exciting product announcements that enable a new class of social apps
• Building Social Apps: Engineers and entrepreneurs share their best practices and strategies for building great social apps
• Open Q&A: Facebook’s engineering and product teams answer your questions

The event is being held at the Concourse Exhibition Center at the San Francisco Design Center. The capacity is limited, the company warns, and it’s expected to sell out quickly.

Attending costs $400 if you’re able to do so, but it will also be broadcast live on the web at f8.facebook.com.

The last f8 took place in Spring 2010, and unleashed Facebook’s Open Graph and social plug-ins across the web. It was a pretty big deal.

So what’s in store this time around? Facebook isn’t saying yet, but there is plenty of speculation.

As we’ve heard before, the company is expected to announce some new music-related features. InsideFacebook also speculates that we may see the launch of an iPad app and/or HTML5 mobile gaming details, as well as mobile photo enhancements.