The best HoT cleric got is also the best HoT Sham and Druid got http://www.thehiddenforest.org/spell.php?id=8464 Chaotic Elixier , but realy now when do you think a Regen spell would have been absolutly necessary besides maybe when it comes down to lvling.
The only time i think a Regen spell would come handy is when the group would take permanent dmg due enviromental dmg like Lava in your normal boss fights where melee take rampage dmg and depending on additonal AE dots/dmg it wouldnt help much with caster health regen either.