What bots are in demand?

I've been making bots for a little bit now, mostly for personal use. However, I'm only a mid-level, and I'd like to start making bots I can sell. So- what sort of bots, simple or complex, are wanted, and how much can one sell for?

 

See what others are selling for here:
http://sythe.org/forumdisplay.php?f=594

See what people are requesting here:
http://villavu.com/forum/forumdisplay.php?f=94
(And other forums with a request section)

 

I've visited both of those, but I find it's helpful to ask a question directly as well as doing indirect research.