You can find the Rogers roaming rates for various countries
here
Basically it's $0.05/KB most places (at least in my experience.) I had thought it was only $0.01 in the US, but I just checked and it's also $0.05 there. Data roaming outside the US is relatively expensive because of the way they round up to the 10K mark. I find that my data usage about triples as a result.
I don't get _tons_ of emails, but I still find the $90 plan is best for me. Even a minor bit of web browsing pushes me into several MB/month.
Check out
www.howardforums.com for lots of Rogers and Blackberry info.