The shadow effect in Jackie Chan always impressed me, even moreso now that I know how it was done. Clever abuse of the VDC's priority system.
Dead Moon's final boss. The game has pretty awesome line parallax throughout most of the game, but that final boss is just awesome... the fast-paced parallax scrolling and the sheer number of on-screen sprites (especially if you use the green or blue weapons), coupled with the intense soundtrack, make it an cool, unforgettable event.
At least to me anyways, hehe.
Not a lot of tricks really, just the line scrolling, but there's virtually no sprite waste, something that some other lesser horizontals screw up with even less going on.