I can 2nd DevilsFan's comment about the Givi 47 liter top case (V47N I believe is the part number for the one I got).
Its pretty basic but holds just about everything I need on a daily basis and fits my laptop inside a leather carry bag flat on the bottom. Its easily the most useful "mod" Ive made on the bike so far. My only gripe with it is I wish that there was some kind of net for inside of the lid. Although there is a wire rack Ive been eyeballing (part no. E159) and I would imagine that you could probably rig something up with the screw mounts.