Dava picks. I just mentioned them in another thread but wanted to post them here. I have arthritis in my picking hand (thumb in particular) and was having problems with the pick flying out of my grip while playing.

My local guitar guy steered me to Dava "grip tip" picks. The picks have a nubby, rubber coating that really enables me to hold onto the pick. They also choke up really well, so the pick I'm using for strumming can shift to lead duty pretty ably.