Places like Newegg and Tiger Direct I've had lots of positive experiences from. They're large enough now to cater to the customer despite being an online vendor.
I've actually returned/exchanged from NewEgg before and it was hassle free so I'm prone (and perhaps biased) to use them for most of my I-can't-find-it-at-Best-Buy needs... hehe
Though I will admit,
Astro pointed me to this and will probably be my next adventure non-mac related.. hehe
http://us.shuttle.com/