Q: Can you plug your iMac into European 220v without a transformer

I think they are all auto-adapating now but you can double check by reading the label that is usually on the Mac or the cable.  What you might need to buy is a converter for the plug itself.

You just need to change the plug or have a plug adapter,  it will auto switch.

http://support.apple.com/kb/HT1981

Just to add the gory details - your iMac has the transformer built-in. It accepts 100-240V 50-60Hz which covers most of the world. All you need is a local power cable or a plug adapter.

This actually helps me considering I'm going to Sweden in Summer. and maybe i can bring my mac over. All I would need is a cable. Wow.

And a big excess baggage bill!

Also note that a plug adaptor, which you can probably buy at the airport, will fit all European sockets, except in the UK.