I had a lot of fun with Dragon Egg from Masaya. You play as a girl who is in possession of the last dragon egg in her world, which she uses initially as a means of attack, but with power-ups, the egg will gradually grow into a full-sized dragon which she can ride. It's pretty fun, tried-and-true platforming, but can be beaten in under twenty minutes if you know what you're doing. I'd recommend it if you see it for cheap...I think I paid a little over $30 for mine complete.
Another person mentioned Momotarou Katsugeki, and I second that. Classic gameplay, colorful graphics, and great personality to that one. Plus, it's so cheap!