Seven? Arr, that be killin' me. If they have to be RPG books, then maybe:
The complete* d20 SRD, nicely set out and bound.
Earthdawn Classic (maybe - don't own this yet; this is just a whimsical optimistic 'vote').
Beast Builder
CoC
some book of the planes or other.. not sure which one.
some large-scale sci-fi system... not sure about this one either.
All my house rules & setting notes, all in one place, printed and so on.
* inc. d20 Modern etc.
If they didn't have to all be RPG books, I'd include some whopping great hardcover monster of a world history book (if there's a good one out there), and at least one or two other bloody big non-rpg resources.