Note: I get no referral fees and these are places I’ve used to purchase my own equipment. Another place to look for recommendations is Photo.net’s neighbor to neighbor section.
B&H is simply the best place to purchase equipment online. They have a large selection, excellent prices, and good service (i.e., excellent return policy). This is the first place I check when I need to buy something, and I recommend them without reservation. Another good store is Calumet, but they are usually a little more expensive than B&H.
Keeble & Shuchat in Palo Alto is my local camera store. They have a nice selection of goods but they can be pricey. However, they are one of the few places in the peninsula that actually carries professional equipment. They have a large sales staff and who are usually very helpful.
NewEgg is primarily a vendor of computer equipment but they carry inkjet printers and low end digital cameras. They have a very good reputation and excellent prices, but like most computer equipment sellers I believe they have a restocking fee for returns.
I use A&I for slide processing and they do an excellent job. They are fast and cheap and it costs about $5 per roll of 35mm film with mailers. If you send in enough film at once, they will ship it back priority or even Fedex it. However, they use cardboard mounts which is inconvenient for scanning. I haven’t used A&I in years because I switched to digital a long time ago.
Ebay is really great for selling camera equipment and I found that I can get very good prices for my used gear. I have also bought equipment, but I believe this is much riskier as you cannot see the goods beforehand. I have primarily bought low cost cameras such as my minolta autocord ($80) and an old Polaroid land camera ($15). I would hesitate to buy anything more expensive here.
Acratech makes an excellent ballhead. Really Right Stuff, Kirk, and Wimberley make a variety of Arca-Swiss plates, flash-brackets, and other miscellanous equipment. All of these vendors have good reputations, and I’ve had good experiences with all except for Kirk (because I haven’t bought anything from them yet).
I have read many recommendation for KEH as a place to buy used camera gear online. For newer gear, their prices seem to be high and can often approach what one would pay for a new item at B&H. However, less popular items can be inexpensive. I have not bought anything from them yet, although I’m tempted to purchase a used 28mm PC Nikkor from them.