Seeing the Imperial Aces pack - which is essentially more Tie Interceptors - and several 'possible wave 4+' threads below led me to wonder what else you'd put in...
The key thing is finding pairs of ships with a theme, and not going too far off into the realms of obscure ships; people want the iconic things they recognise.
The only one I can think of is the Z-95 and the TIE Defender.
Sounds a bit odd, but my argument is that the Z-95 is a Rebel fighter which behaves like an Imperial one (low armament and swarmy), whilst the Defender is an Imperial fighter which behaves like a Rebel one (well laser-armed and shielded). They're also both two of the most-recognised designs which never turned up in the films.
Any other pairings people can think of?