Here is how I rank the major powers. This does not count non corporeal beings. I have added done delta quadrant species in. This is how they stand around 2371.
1st tier( Galaxy spanning projection overwhelming military might)
Borg
Dominion (maybe between a 1 and 2 as the dominion can't go transwarp)
2nd tier ( large military might with diplomatic and economic influence over a large section of there quadrant)
Federation
Romulans
Klingon
Krenim imperium
Devore
3nd tier (regional power with significant influence in there surrounding area)
Tamarians ( maybe 2nd tier)
Cardassian
Ferangi ( I get the impression they are a economic power, however they have no centralised military instead relying on defence contractors and warships in private ownship with first line of defence being to useful to everyone)
Breen
Tholian
Tzenkathi (they appear to have given the feds some trouble in a war)
Bo'mar
4th tier ( regional power with limited influence)
Gorn
Talarian
Talaxians
Kazon
Vidian
Pakleds
Lysian
Satarran
Mokra
5th tier ( single system civilisation with limited significance)
Bajorans
Acamarians
Antedian
Angosians
Anyone care to add more?
1st tier( Galaxy spanning projection overwhelming military might)
Borg
Dominion (maybe between a 1 and 2 as the dominion can't go transwarp)
2nd tier ( large military might with diplomatic and economic influence over a large section of there quadrant)
Federation
Romulans
Klingon
Krenim imperium
Devore
3nd tier (regional power with significant influence in there surrounding area)
Tamarians ( maybe 2nd tier)
Cardassian
Ferangi ( I get the impression they are a economic power, however they have no centralised military instead relying on defence contractors and warships in private ownship with first line of defence being to useful to everyone)
Breen
Tholian
Tzenkathi (they appear to have given the feds some trouble in a war)
Bo'mar
4th tier ( regional power with limited influence)
Gorn
Talarian
Talaxians
Kazon
Vidian
Pakleds
Lysian
Satarran
Mokra
5th tier ( single system civilisation with limited significance)
Bajorans
Acamarians
Antedian
Angosians
Anyone care to add more?