BFG's got a solid customer service department, and you pay a premium for it.

Thermalright's customer service email is a very fast response (about 6 hours or so, 24/7). ASUS has a bit of a slower customer service email response, but they know exactly what they're talking about. I'm not sure if Hercules is still around in a big way (this was back in the Kyro II days), but they've got some of the best phone support that I've ever encountered in a computer-related field ... <5 minutes on hold to an 800 number and speaking with someone who's first language is English? Incredible!

That, and my problem was troubleshooted very quickly by a very knowledgable tech -- it had something to do with the differences in AGP specs along with memory controllers on particular motherboards under Windows 98 ... I don't even remember it anymore, but I remember the experience, and given the chance to purchase another product from them, I won't hesitate because I'm afraid of the customer support issue.
The only product that I've ever RMA'd has been an incorrectly labelled product back to NewEgg, and it was a bit of a hassle (since the sticker on the wrong product matched the code for the product I wanted, if that makes sense), but everything was eventually straightened out OK (minus shipping). Guess I've just been lucky.
Retailers? DealSonic (
http://www.dealsonic.com ) has one of the best customer service departments for an etailer that I've encountered.. Email response within 3 business hours? Telephone number where people actually answer? That and they go the super-extra-mile to please their customers. This is all second-hand, unfortunately, as I've never had to deal with an RMA with them since everything's been great from initial order with them. They don't have a gigantic selection, especially of top-of-the-line-just-came-out-today merchandise, but they're the first place I look when I'm going to buy computer stuff online and I haven't been disappointed with them yet.