I'm not really into the unifroms themselves, but more into the girls wearing them & the materials they're made of. But I'll give a few examples of what I like (If the criteria mentioned above apply),
Nun,
french maid,
burglar ((preferrably black spandex) catsuit and mask),
nurse,
superheroine,
Stewardess,
Cop,
School uniform (only if the girl wearing it doesn't look like she's nearing 30... that just looks silly, but is sadly often the case...)