I loved the C64 (and my eventually '030 expanded Amiga B2000).
I played the hell out of Lode Runner (and on Amiga) and Archon / Archon II.
The others on this list didn't grab me as much.
Other C64 titles I remember I played a lot were:
- The Bard's Tale set.. I have a sneaky suspicion I have some of the maps lying around in storage somewhere.
- Zork series (I recall getting a guide via a BBS back in the day)
- Paradroid (and Paradroid 90 on the Amiga)
- International Karate +
- The Boulderdash series (and constructor kit... sharing levels back and forth with friends)
- Commando (another title with Rob Hubbard's musical magic tricks with SID)
- The Pitfall games
- Elite (and now Elite Dangerous on PC)
- Arkanoid / Arkanoid II
- Green Beret
- Wizardry games (I didn't play the Ultima games until the Amiga)
- Spy hunter (having played this well before seeing Blue's Brothers, I thought it freaky they were using game music - ah naive young me)
- Pole Position (I think there was a sequel but I don't recall if that was the C64 or Amiga)
- Ghost'n'Goblins
- The Monty on the Run games
- Nebulus (with some clever overlapping of colour and mono sprites for better resolution)
- The Sentinel (and my book of oh so many level codes - I have never found a satisfyingly playable PC port but the Amiga had a good one)
Some I really missed finding good ports on the Amiga (but then I had a ton of other choices on the Amiga too)