Just found this list, but don't know how up to date it is. There aren't too many 300' tall coasters in the world:
Intimidator 305, Kings Dominion, Doswell, Virginia, USA - 305'
Millennium Force, Cedar Point, Sandusky, Ohio, USA - 310'
Steel Dragon 2000, Nagashima Spa Land, Nagashima, Mie, Japan - 318'
Tower of Terror II, Dreamworld, Coomera, Queensland, Australia - 377'
Top Thrill Dragster, Cedar Point, Sandusky, Ohio, USA - 420'
Kingda Ka, Six Flags Great Adventure, Jackson, NJ, USA - 455'