I need to ship a frame back to the shop in Italy where I bought it. Anyone got any suggestions for the best-value way to do this? (At the moment the best I can find is a cheap Easyjet flight with me on it...)
try parcel2go.com - they check a few couriers and come up with deals that you often need an account to get. I've used them a couple of times both domestic and to Spain and found them to be excellent. A tip is to make the packages as short as possible as a lot of couriers don't carry packages beyond a certain length (can't remember what it is though).
I use www.interparcel.com I recently posted a 12kg set of Husqvarna motox forks to Greece for £48, worked out using volumes and weight instead of just size alone. Interparcel use other couriers like UPS and DHL, and they offer a great service. The website is simple to get quotes from too. Never had any issues using these people.
I had to move quickly and ended up using UPS. For info, it cost £100 to send a frame weighing 1.1 kg (plus packaging) to Italy, so it sounds like they're very expensive compared to the sources you suggested.
Live and learn!