The website sizesquirrel.com is handy for finding other shoes based on your current size in a certain shoe. I find it best to read other profiles rather than rely exclusively on their analysis of the size.
EpicTV also has a basic tool on their site where you go to the shoe you want, put the shoe and size you have, and they suggest a size. It's good to get a general idea of brand size differences (eg Scarpa = La Sportiva EU size +1) but I'd supplement with Size Squirrel to get more detail on fit.