Most druid transmutation spells are buffs or spells that have no saves making the Druid capstone underwhelming when compared to others. Here is a couple of very useful spells that I'd love if druids got them.
1. Baleful Polymorph Drd level 5 spell. Fortitude/Will save or be turned into a harmless animal. Basically the single target version of Mass Frog.
2. Gorgon's Glare Level 9.. Medusa petrification cone, Fortitude save.
3. Single target Encase/Flesh to Stone/Petrification. In game druids cast this one. Halsaime petrifies the harper in the beginning of the end fight of Druid's Curse.