With Euros I'm really not sure of any sites that help you find pricing info. The main thing I do with change is first look for coins in uncirculated condition, basically straight from the mint. They may or may not go up in value, but not a bad bet to hang onto. Error coins are some of the best to collect, when the coin has a defect from the minting process. Those have been some of the best finds I've come across since most are caught by the mint before release. Another thing to look at is how many were made, some years mints have problems and can't produce as many of a particular coin, they will tend to be more expensive.

I wish I knew more about collecting Euros, here in the US you just don't see that many.
!PIMP