We did a whole school Read a Thon last year to raise money for Classroom libraries. We invited tonnes of people in, from local "celebrities" to parents to politicians. The kids loved it (and I was teaching grade 7/8!) We had out local MPP (Member of Provincial Parliament) and he was amazing - the kids adored him!
I've brought a few other people in to discuss their careers and how they got their as part of our Pathways program (goes from gr. 7-12, so at my end it's just to get the kids thinking about all the different types of careers available, and getting them thinking about their strengths and what types of areas they may be interested in, and what they should be looking at in highschool to get to those areas). Everyone from DJs to lawyers. The kids always enjoy guests in the room.