Since Jcp mentioned Tangrowth, I figured I'd post one of my favorite combos in this metagame and a Regenerator core superior to AmoongBro:
Tangrowth + Slowking.
Like Jcp said, Tangrowth is a boss. I've been using it since Excadrill days and it is just incredibly reliable; tanks physical hits like no tomorrow, and between Leech Seed and Regenerator, it never dies. Unfortunately its SpDef is beyond bad, it absolutely blows.
Slowking is a hell of a great rain counter; for example, Choice Specs Keldeo's Hydro Pump can't 2HKO...that's impressive. It's got reliable recovery and
Regenerator. Too bad its physical defense is below average, but Scald's burn rate helps with that to some extent (screw you Scizor!!!).
This core works best with multiple entry hazards because they force loads of switches and Slowking can phaze with Dragon Tail; I personally like Forretress for this role because it can set-up any hazard I want and can also Rapid Spin; even though this core doesn't mind Stealth Rock as much as other physical walls, Toxic Spikes are still a bitch and it's just much easier to wall things when you come in and take damage before you even get hit with an attack.
Overall, Tang + King is an incredibly solid defensive combination, give it a shot.