I also wasn't sure what to ask people for as we'd brought most things ourselves and consequently we ended up with a lot of stuff we didn't use and I felt even worse (e.g. baby towel sets and baby washes which we don't use (organic is so much better for my bubs skin and available from normal supermarkets for not much more)!
I really wish I'd ask for people to put some money towards photos. We paid for a professional photographer to come to our home and do a shoot which was about $200 for the shoot and then photos on top. I thought it was a bit pricey to start with but friends have done the pixie photo thing and have ended up paying just as much and the shots we got were so beautiful and I made thankyou cards with some of the shots. Just a thought.....