Mobile app developers are most looking forward to developing new apps for Android, Windows Phone 7 and the iPad, according to a report released today by mobile ad network Millennial Media.

The firm, together with technology analysis site Digiday and an analyst from Stifel Nicolaus, surveyed app developers, publishers, and advertisers in the most recent quarter regarding their plans for 2011 and their practices this year. Since most developers already have iPhone apps, it’s interesting to see what other platforms they’re interested in.

It’s no surprise to learn that Android may see the biggest growth next year, but it’s nice to have actual numbers from developers. 29 percent of developers said they would bring new apps to Android next year, while Windows Phone 7 and the iPad tied, drawing 20 percent of developer interest each.

Android could very well overtake the iPhone’s developer lead by next year. 30 percent of developers reported supporting the iPhone in 2010, compared to 23 percent for Android. Millennial also notes that the iPhone (along with RIM) saw a year-over-year decrease in developer support, which will also work in Android’s favor come next year. 8 percent of developers plan to launch new iPhone apps in 2011.

Developer interest in the iPad is likely tied into overall interest in the tablet format, something that will also benefit Android-based tablets come next year.

It’s also worth noting that Palm made out the worst when it came to developer interest for next year. 4 percent of developers said they would pursue Palm’s webOS platform — even the embattled Symbian platform scored higher with 6 percent.

Publishers are also confidant that their apps will take off next year. 31 percent anticipate a 100 percent or more increase in revenue from their apps, while 17 percent expect a 50 percent or more increase.

When it comes to choosing a mobile platform to support, both advertisers and developers consider reach, demographic and better branding as their main considerations. Millennial reports that both developers and advertisers are also taking an increasingly cross-platform approach — not a surprise given that reach is their main concern.

The big takeaway here, yet again, is that Android is set to explode next year. The interest in Windows Phone 7 is certainly a surprise, though. It’s possibly a sign that Microsoft has managed to make developers forget about its dead Windows Mobile platform and has made them believe in Windows phones once again.