An overbed/hospital bedside table works wonderfully for that. I use a straight one: http://www.amazon.com/Invacare-Over-Bed-Table/dp/B000QA0EHI but there's also tilted ones: http://www.amazon.com/Hospital-Overbed-Over-Table-Computer/d...

For $50/$60, you get an adjustable, rolling table. It's not the sturdiest ever (e.g., I wouldn't put a monitor on it without gluing it somehow), but if you're using a laptop, this thing is perfect.