I think its a lot of fun to stuff your SMC with emulators and games - As the man above said, try ones that you have never heard or played before - You might be surprised as to how many great games are out there.
Frodo and GPeng are excellent - Try Bubble Bobble, Impossible Mission, Willow Pattern, Nebulus (another good choice sir!), Encounter, Uridium, Paradroid, Ikari Warriors, Action Biker, Kikstart, Thunderbirds (Firebird version) - All on the C64 - I could go on with suggestions but I can't be bothered as its the day of rest (!).
I'm soon to be upgrading to a BLU and I have had a quick play on it and the difference is amazing - So I can see me playing on this unit a hell of a lot more!