P2W vendors sell two, for a million each, which are both permanent and share a 60 min cooldown:
Renewal of Light rezzes you to half health, and blasts the critters around you with knockback and a debuff.
Return to Battle rezzes you and grants the effects of all the Large Inspirations (sort of like when you level up). So, effectively full health.
As Wolf mentioned, Events and Bank mishes can grant temporary self rezzes, which I think have their own cooldown.
And don't forget a large Rez, Breakfree, Heal and End insp in quick succession are pretty damn effective! Stack 'em vertically and hit, e.g., F1 four times fast and you're back in business right away!
I speak from ignorance here, but rumor hath it that an Incarnate power choice includes a self-rez.
(Edited to add: I think Techwright beat me to it, but IIRC, the Day Job power from AE only works in AE missions?)