Looking for theme ideas?

I've come across the Weekly Shot blog, which is good for ideas and inspiration on what to photograph. They have a weekly theme, which for this week is "Trees", and last week was "Look Up". Joining the group is by invitation only, but there is a link to a sister site called Vazaar, which will eventually be open to everyone. So if you are looking for a challenge to help you improve your photography, check out both sites for ideas.