Since I haven't the means to afford any sort of theme park trip to Europe or Asia at the moment, here's my top 10 North America-centric, somewhat-realistic wish list:
1. Bizarro (SFNE)
2. Voyage
3. Boulder Dash
4. X2
5. New Texas Giant
6. Prowler
7. X-Flight
8. Beast
9. Leviathan
10. Superman: Escape from Krypton
These aren't necessarily the 10 best coasters that I've yet to ride, but some of them (such as Beast & S:EFK) are ones that I've coveted for a long time, even if they're overshadowed now by newer, superior coasters.
If I had to pick the top 10 international coasters I want to ride the most, they'd be something like (in no particular order): T-Express, Mountain Flyer, Shambala, Nemesis, Walibi's Goliath, Eejanaika, Dodonpa, iSpeed, Katun, and Oblivion.