Ooh, just thought of another one. Thanatos on the ZX Spectrum.
Edited to add details:
You play as a dragon, or more to the point, as someone who has been turned into a dragon. You then have to fly from left to right (although you can go right to left, but all that seems to yield is massively more dangerous monsters) fighting a variety of enemies (soldiers, giant spiders, sea serpents, giant bees, etc)using your fire breath or by picking them up by skimming over them with your claws open. Your goal was to fly to three castles, first to pick up a sorceress, then to pick up her spell book, then to drop her off at a cauldron to turn you back into a person again. Problem is, your fire breath ran out, so before you could burn down the gate to the second castle you would have to eat a witch to replenish your fire. Thing is, the witch was guarded by a knight, he killed you pretty quickly, and it was practically impossible to actually eat the witch. Thus I never got into the second castle. Loved it though, althought the sea serpents probably contributed to my fear of deep water after dark.
Here's the video of it:
http://www.youtube.com/watch?v=VruAncI6XzA
It's harder than it looks.