The par-3 7th at my home course, Tedesco, is listed on the card at 239. It is downhill to a very small green surrounded by two large bunkers, with a pond down the entire left side, and a busy street over the lefthand greenside bunker. This hole is what I would call a par 3.5, as one day I played it last year, the back tees were way back, and the pin was on the back of the green, and I calculated the distance to 261, the longest par-3 I've ever played.
Honorable mention: No. 3 at Myopia is 253, which sometimes plays longer than No. 6, a par 4 listed at 260 on the card.
--Brad