Recently picked up Final Fight 3 and I have been amazed. Elements of street fighter and double dragon and great gameplay. Best of an amazing series I never knew about growing up. I have played the ones that get the most discussion. Final fight series, TMNT turtles in time, knights of the round, super double dragon. Really enjoy Batman Returns as well and that doesn't get a lot of recognition. Branching out from NES collecting to SNES, I have really enjoyed the beat em ups on that system. Any others outside of what I have listed that I should be giving a shot?

Ninja warriors (although it may not qualify as your typical beat em up)
King of dragon is an absolute must

Sonic blast man 2 is good
Captain commando as well
I'd check peace keepers and brawl brothers as well when im done with all the above.

Legend is supposedly good but only played it on emulator and couldnt understand the mechanics... will have to give it a go on my snes.

You did not name in your post but inassume you already lnow of battletoads in battlemaniacs.

Then you have maximum carnage and death and return lf superman.

Have fun

I like combatribes. There are better ones but for some reason it's one of my favorites to play.

Knights of the Round & Power Rangers The Movie are the best ones IMO

I have seen video of ninja warriors and it does look great. I have battletoads/double dragon but not battlemaniacs. Have to check that out. Captain Commando keeps coming up in Ebay recommendations. Been meaning to YouTube that. And I have sonic blastman 1, but not 2. First 1 I found pretty uninspiring. I assumed 2 was the same, but with the option to play 2 players. Let me know if I am wrong. Seems like a really good list. I'll check out the others - thanks.

Check out "Ghost Chaser Densei" & "Undercover Cops". They never left Japan, so I thought I'd throw some more obscure ones out there!

That is two carts that have been alluding at the moment, kinghts of the round and king of dragon = / / /

Yeah, as with other people, I agree with King of Dragons. It's the 2nd best beat 'em up on the console imo.

Is King of Dragons hard?

I second MMPR The Movie on SNES.

Not really... straight forward mechanics and the game seems to be designed to get pretty far on the amount of lives and continues given. Might take a few times to beat it.

Pirates of Dark Water is another beat 'em up that rarely gets mentioned. Slightly uncommon and I would say on the better half of the genre for the system, but not as good as TMNT, Ninja Warriors, Captain Commando or KoD in my opinion. Even though it's slow, the first Power Rangers game is pretty fun. The Final Fight series are always easy go-to games as well.

Seperation Anxiety is alright.

The original is only a 1 Player game though, MMPR: The Movie is a 2-Player Co-op game and much improved

I actually got Power Rangers the Movie in the same purchase as the FF3. Haven't played it much as I am hooked on FF3. I tested it out and was frustrated you can't move freely on the screen and didn't love bouncing level to level. The powerup feature seemed cool though. 

Knights of the Round is up there in my favorite games that I picked up in the last few years. I have put too many hours into that game. Strangely, I played SNES growing up, but I never played any of the games in this category. Weird because most of my favorite NES games were beat em ups. I just didn't know anyone who had or played these games outside of TMNT. Its been a blast finding them later in life. 

Stone Protectors. People think it is a TMNT clone, but it's actually a lot more and it has a lot going for it.

Rushing Beat Ran/Brawl Brothers is almost Streets of Rage 2 levels of good.
Check it out.

Legend

Those last three suggestions look awesome. Nice to see one with a low pricetag in brawl brothers. 

Stone Protectors is... definitely a video game starring boy Troll rock stars...

Brawl Brothers is grossly underated. The other games in the series, Rival Turf and The Peace Keepers, are OK too, but BB is the best.

Do you have a Genesis? There are several good ones on there as well.

Braw Brothers also is sort of a 2 per 1 deal.
It sports many differences to Rushing Beat Ran, but using a cheat code you can actually turn it into Rushing Beat Ran, allowing you to play the JP port without the mazes and with some different combo possibilities.
Keep pressing b,a,x,y during the Jaleco screen to unlock the JP version.
 

Thanks, Bea. Will definitely be picking that game up and I'll give the code a try.

Teluin, no genesis. Until recently I had a buddy in the area with one and a decent collection. We played lots of hyoerstone heist. Hate to admit he was right it was better than SNES TMNT

Neither especially hard but they are quite fun, so if you're ok with SFC games there are Bishoujo Senshi Sailor Moon (and sequel Sailor Moon R) which are you're fairly mid-period generic brawlers that are fairly amusing but not overly hard either.

Already listed: Combatribes, Brawl Brothers, Stone Protectors, Final Fight 2, etc. I will just add that Return of Double Dragon >>> Super Double Dragon (Japanese version versus American version). Damage levels are better in JP version, special moves operate differently, etc.