Portfolio App for Ipad
There's one called My Proofs which recently had an overhaul. I haven't checked it out since the overhaul yet.
If you have a Zenfolio account, there is a Zenfolio app you can use.
Will you have wireless access to the internet? If so, having a website optimized for mobile display would probably get you what you need.
I don't use any myself, so I'm curious to see what others have to say.
A while back there was an article posted to this site comparing several products. You might look for it. There are most likely comments to that article suggesting other products, too.