See this post here on HUBB, it has all the information you need: Here is where you get the cheap European green card insurance
I am aware of two options that are available to the "not from Europe" rider who plans to bring a bike to Europe and ride around.
1) If you plan to stay within the EC countries, then the 22 Euro a month liability coverage from Arisa is all you need. If you plan to perhaps venture out of the EC to only one or two other countries, then you can cope with the unique insurance requirements of those countries at the border crossing.
2) If you plan to do extensive travel in countries that are not part of the EC, then consider getting liability insurance from Motorcycle Express
. They provide the same level of coverage (minimum legal requirement for liability), but their policy is good in just about every country from Iceland to Israel. Heck, it's even valid in Iraq, not that I would recommend you plan on riding through there.
The policy from Motorcycle Express is considerably more expensive (about USD $120 a month, I think) but it covers twice as many countries, thus, it is a better buy for someone who plans on doing extensive travel outside of the EC.