For DVDs (in order of preference),

DVD Pacific - Great prices, great service, stuff comes early, cheap media-mail shipping

Deep Discount
- Great prices, free shipping, slooow shipping, OK customer service

Amazon
- Variable pricing, slow "super-saver" shipping, good customer service, the best everyday price on Blu-ray

For imports

Xploited Cinema
- Good prices on imports, super-fast shipping, excellent service, great selection