<PERSON> and <PERSON> - <PERSON> was an unqualified miracle product of this experiment, but the program was shut down during TFA after <PERSON>'s death. SSR probably held onto the secrets of the program and possibly transferred them to SHIELD, but both may simply not have had the genius to get it working again. SHIELD was also notably edgy about giving any one person too much power. The U.S. Army apparently got a hold of the Super Soldier Serum because they used it as part of the Gamma project.
Gamma - Bruce Banner was the only true success, but his creation was an accident that nobody has been able to replicate. Abomination is mostly useless. Last we heard, the Army has him locked up, but he hasn't popped up again since TIH for a reason. 503
The Leader popped up briefly in TIH, but it was never made clear if he was empowered by Gamma or just made crazy by it.
Extremis - Awesome stuff, but it can make your "super soldiers" blow up, so not that useful if you're not a terrorist organization willing to sacrifice dozens of subjects to find one that doesn't die from being injected.
Centipede Serum Of course, Extremis is then commandeered by Hydra along with Super Soldier Serum (presumably taken by one of many double agents from SHIELD) and <PERSON> (I guess they've got double agents in the Army, too, woooo!). Mix that with blood platelets from Scorch to keep everything from blowing up, and you've got some power. Too bad your soldiers need massive energy infusions every few hours and ridiculous amounts of rest. So in a lot of ways, they're worse than regular soldiers. No wonder nobody uses them.
Too be fair, <PERSON> (aka <PERSON>) did figure out how to stabilize Centipede Serum with GH 325, but <PERSON> has the stuff locked up and he's probably reluctant to use it until he figures out why it's making him go mad.
All in all, nobody's making super soldiers because it's too hard. Not that that's a coincidence. All these stories would suck if there actually were a million Captain Americas running around, so the writers keep that from happening. 837