Actually it's dead simple once you stop thinking of it as transferring photos and realize what you are doing is syncing what you set up on the computer.
Create one master folder for your iPad pictures. Create one sub folder in that folder for each album you want, and copy the pictures to those folders. When you select to sync photos in iTunes, pick the master folder, then choose Selected Folders. Check all the folders you want to sync.
When you want to add pictures, either add them to the existing folders on the iPad, or create and select additional sub folders. Then sync again.
The idea is to create and maintain what you want on the computer, then let the iPad duplicate it.