Whenever I ship a package, I struggle with finding the best price. I go through the steps and fill out the forms on FedEx, UPS, DHL, and the Post Office's site. It's cumbersome and a royal pain.
Just recently I've started exploring shipper comparison sites and boy has my shipping life become easier.
RedRoller compares shipping rates of the Post Office, DHL, Overnite Express, and Eastern Connection. Of course it'd be more practical if they included FedEx and UPS, but hey, I don't own the company, so what do I know...

RedRoller compares Post Office, DHL, Overnite Express, and Eastern Connection
The second shipper comparison site I tried is Iship which handles DHL, UPS, and the Post Office. That's better, but like RedRoller, it's missing FedEx. I suspect that's because Iship owns UPS and there's no way, no how they're going to let the RedRoller competitor display their rates.

Iship compares DHL, UPS, and the Post Office rates
The almost hands down winner is Shipping Sidekick because they handle the four services I use the most: The Postal Service, UPS, FedEx and DHL; Shipping Sidekick is also fairly easy to use.

ShippingSidekick is easy to use and handles all four shipping services
Of all the Web service I'm using, though, ShipGooder is the fastest and easiest, and handles the four services I choose from the most -- the Post office, FedEx, UPS, and DHL. Loyal reader Mande Gianfala told me about ShipGooder and said, "As a programmer, I also love the AJAX interface; the courier rate quote results are instantaneous." I agree. And thanks, Mande!

ShipGooder is more comprehensive than the rest -- and way easier to use
Thanks for mentioning RedRoller in your post. We’re glad you like the site, and invite you to keep coming back as we’re making changes to improve the site all the time. One of our features you may not be aware of is that RedRoller is the only one of the four services that allows customers to print the actual shipping labels (not just an estimate). I would love the opportunity to walk you through some of the other features RedRoller has if you’re interested.
Mark Taylor
Chief Logistics Officer
RedRoller