I'm going to miss you by about a week as I am leaving similar trip next Friday
Anyway, there are heaps of good rides. Croatia / Montenegro coast if you can get that far south. The road from Montenegro to Sarajevo is meant to be fantastic.
Rather than me tell you heaps, there is a site Welcome to Motoromania.com - Your online guide to motorcycling in Romania that has a lot of good routes there. I'm sure others can pitch in on places and sights.
Don't have as much info on poland. Loosely route we are taking is London - Ancona -> Split (ferry) -> Budva -> Mostar -> Sarajevo -> belgrade region -> Pitesti -> Sibiu -> then back across northern serbia / croatia - slovenia austria etc. on the wya home.
Here is a rough map I drew Google Maps
|