Unsuccessful app? sell it

There's an on-line market for app developers you might want to try:
http://www.apptopia.com

You might get lucky (or not).

Which SDKs are popular in the Android Market?

It's always good to know which SDKs are trending, and which are niche player. Few weeks ago I found a site that created statistics on the Android Market just for that:
http://www.appbrain.com/stats/libraries/dev

I found it very useful. Hope it helps you too.