Have you seen this?
http://www.amazon.com/gp/product/B00...A3NDZMWLDIE8HQ
I've only seen it online, so I can't say whether it's any good.
In the past, I've also seen breakfast trays for beds that include book holders with adjustable angles. I don't own one of 'em, though.
I use cushions, cheapo picture easels. I also just dug out a cheapo easel I bought at a drugstore months ago. It adjusts to many angles and weighs next to nothing. I think it was meant for netbooks. I picked it up because it looked like it might be handy one day, and now it is.