I've found USPS to be excellent for frames and smaller- usually $20 domestic with delivery confirmation on steel frame and fork. The best deal For small stuff is USPS priority for around 4 and change with deliv conf gets across the country pretty fast.. For complete bikes Fedex ground can be cheaper than ups but with all those UPS stores as dropoffs and you can get the counter rate directly from paypal I've been using ups mostly but once the FEDEX takeover of Kinkos takes place then suddenly Fedex becomes pretty convenient.