I usually slot Stamina (in order of utility):
(Corrected thanks to Maelwys!)
Performance Shifter proc (gives END)
Performance Shifter END Mod (increases Stamina)
(Also, having both increases Movement speed by 7.5%, but that's irrelevant)
And in Health (again, in order of utility):
Panacea proc (gives END and HP)
Numina's Convalescence +END +HP
Miracle +Recovery
(Is it weird that the best END mods come from HP enhancements? Yes, yes it is. This is CoH, where the temp power Tough Hide gives you +Defense, and there are bus stops but no buses.)
Panacea can be pricey, but the two Perf Shifts aren't too bad. Run missions, explore zones, get Merits. At an ATM, trade Merits for Enhancement Converters, sell Converters on the Auction House, you'll afford the PS ones in no time.
Once I have it slotted that way, along with the Health ones Moon recommends, I don't worry about Stamina unless I'm fighting Malta or Carnies. (Which I love to do; many players are scared of them; I find them a welcome challenge!)