I love challenging myself as well
At the moment I am working on Affairs of the Heart, which has been a work in progress for the last 18 months, I am hoping to get it finished for my guild's show next year.
http://www.amazon.com/Applique-Maste.../dp/157432859X
I am also working on Sea Urchins by Judy Niemeyer, which I hope to finish by the end of this year
http://www.quiltworx.com/patterns/sea-urchins/
I recently made a mini quilt which was fun (never tried one of those before)
http://www.quiltingboard.com/picture...t-t208253.html
This cube quilt was also a lot of fun and it got so many positive comments at the quilt show I entered it in,
http://www.quiltingboard.com/picture...s-t163579.html
If you want something different how about a Bargello or OBW?
Good luck and have fun.