These ideas were submitted for participation in Google Summer of Code.
See the list below about existing ideas you can work on or submit your own using the form further down. You may also want to check out the random ideas page to get an inspiration of what topics you could work on. You can then come up with a more detailed plan yourself if you think one of them suits you.
Other than that there's always the bugtracker as a last resort to check for "missing features".