Well, I'm one of those people who thinks that essentially every episode or film in Trek could benefit from remastering in one place or another (even if it is just to fix little things here and there). However, the only film that jumps out to me that *really* needs remastering is 'Generations' - I realize most of it is fine, but as Kegek
said, the stock footage from TUC needs to go. Let's be honest though, some of the stuff in TOS movies is dated, so I'd remaster all of 'em.
As far as the series are concerned, I really do think TNG needs to be remastered. There are some BAD looking effects in the earlier seasons and there's still a lot of crap stuff in the latter seasons (the blob effect in 'Aquiel,' the ship flying out of the Dyson Sphere in 'Relics,' etc.)
Remastering the movies shouldn't be a problem - they could do like Star Wars did and release both the theatrical and remastered versions in the same case.
Someone probably needs to do a poll to determine how many people would buy TNG Remastered.