Going by that list:
Tin Man - The last of its kind, wandering the galaxy with Tam. Not much of a force to be reckoned with though able to defend itself when needed.
The Douwd - Were interested in peace above all else, grief and anger caused one individual to take action. I doubt they'd be interested in battling anyone though.
The Kelvan - Able to travel across galaxies, so they would probably be a force to be reckoned with--if they wanted to fight that is.
The Prophets - Totally uninterested in affairs outside of their realm--only took action after being pestered by The Sisko.
The Pah-Wraiths - Only interested in revenge against the Prophets.
Species 8472 - They seemed trapped back in fluidic space. It they weren't they would've attacked by now.
The Borg - VOY destroyed them as being a threat, since one solitary ship could defeat them on multiple occassions.
The Hirogen - Nomads, no collective force except for the occassional hunt. Not interested in battle just hunting.
Remans - Their only focus would be against the Romulans, not anyone else.
Caretakers - No clue where they are. Again able to cross galaxies and very advanced, but not much interest in conflict (from what we saw).
Founders - Created the Dominion. Nuff said really.
Humans - Kinda feeble without the rest of the Federation.