Freespace 2 (We've got code- need to get rights for assets for commercial release if possible...)
there is already a pretty mature linux fs2 project underway ( on http://scp.indiegames.us/ ), so that might be a duplicate effort.
PopCap's game framework and PopCap's games themselves.
deus ex really deserves a new port. i'd vote for it.
how are things looking with studios that don't exist anymore? i'm thinking of classics made by bullfrog (dungeon keeper, theme hospital, theme park) or muckyfoot (startopia)