My favourite? I refuse to choose!
Way of the Exploding Fist [http://www.mobygames.com/game/c64/way-of-the-exploding-fist/screenshots/gameShotId,193942/] & to follow IK+ [http://www.allegro.cc/depot/IKPC-IKRemake]
Mercenary [http://www.zzap64.co.uk/zzap11/mercenary.html]
Carrier Command [http://www.mobygames.com/game/carrier-command]
Uridium [http://en.wikipedia.org/wiki/Uridium]
Not to forget Wizball, Bards Tale & sequels (who wouldn't enjoy burning those damn 99 skeletons for major damage?

Leaderboard [http://www.c64-wiki.com/index.php/Leaderboard], Armalyte, Last Ninja, LN2 and a bit later on came Powermonger, always got a real powertrip out of that one.
oh god there's more

Commando, Bionic Commando, Ikari Warriors (Ralf & Clark before KoF) & Guerilla War, Street Fighter (1 that is, and all good following scrolling & 1on1 beat-em-ups in the arcades)
wasn't 'legally' a kid anymore when i spent in excess of £800 on Daytona USA but I was loved up like one
Stunt Car Racer, Pilotwings, Golden Axe, Chase HQ, Platoon, Op. Wolf, Secret of Mana, Chrono Trigger, FF6, Axelay, Biometal(JP) (Probably the only person who thought this game had one of the most effective force devices - must be played on the hardest difficulty), Tatsujin(Truxton), Assault Suit(s) Leynos(Battlefield Earth) & Valken(Cybernator), Rise of the Triads, Shadow Warrior... - oh god I'd better stop
ps. oh and Thrust [http://www.youtube.com/watch?v=Dt44PEIWBRg] & The Killing Cloud [http://amr.abime.net/review_37506]
so sue me for being nostalgic but these were great days even if sometimes it was more 'idea' than execution,
on the other hand though, at least gamers today v. rarely have to deal with contentious collision detection & leaf switches. meh :/