Personally, I think "A Link to the Past" is the most clever subtitle in the Zelda series.
Its effectiveness comes from it use as a double entendre. On the one hand, it refers to "Link" himself as the link to the past. But to what past? Simply put, LttP is a prequel to the earlier Zelda games on the NES, so the game itself links us to Hyrule's past (back in a time when we only knew of those two games on NES--yes, I'm old enough to remember those days
). On the other hand, the title can also be referring to other characters or even to the Triforce itself, all of which are links. Just as Ganon was sealed away in the ancient past during the Imprisoning War, so now Agahnim is the link to this past. It could also refer to the Triforce, which links together the ancient past (IW), the present (LttP), and the future (LoZ+AoL).
If you think about it, it's a much more thought-provoking title than the ones that simply refer to an object, such as the Wind Waker, Ocarina of Time, etc., etc.