If you catch sales then the price difference between 8 GB and 16 GB may not be substantial, depending on your budget. 8 GB would likely be fine for you, but more never hurts.
Avoid the "Mac memory" stuff - it's no different than regular RAM, and is just marked up. Don't feel compelled to pay more for your RAM, either. Kingston and Corsair may be favorites among the Mac community, but they can also be on the more expensive side. Companies like OCZ, G.Skill, and GeiL are just as good (if not better, but that's my personal bias) and tend to be cheaper.