I just ordered a NF scope from Sport Optics. I called back the next day and ordered a set of rings. Both times I have been very impressed with the level of service.
All of the above are great but I have personally done business with Scott at Liberty Optics and SWFA. Scott was a true gentlemen, very helpful, great prices, and great service.
SWFA is semi-local and again, very professional. You won't be unhappy with any of the business mentioned here.
If I just want some cheaper everyone's-got-it item like a rail or a low priced set of rings and I'm not ordering anything else, I usually go through OpticsPlanet.com. They have free shipping on anything over $35 or so. It's hard to beat that.
These are the two main companies I've delt with the most. I've been more than impressed with Scott at Liberty Optics and Doug at Camerland NY. I wouldn't be scared to purchase from SWFA neither. I only hear good things about them.