Light Alliance:
(I am only talking about Earls as most of Counts and Viscount follow Dumbledore and Marquis houses withdrew from politics centuries ago. Dumbledore himself is a Viscount, but he does not hold the Lordship as you can't be a lord and Chief Warlock at same time but regent is allowed. Along with his 5 votes of Chief Warlock, he holds 3 votes for Order of Melin.)
Potters
Bones
Longbottom
Moody
Shacklebolt
Diggory
Fawley
Shafiq
McMillian
Prewetts (Ginny is heir, Molly is a Prewett who ran away to marry someone of lower standing and as such, they would have to give a daughter to Prewetts but after death of Molly's brothers the Lord made that daughter who was not yet born, the hier)
McKinnon (on the verge of extinction with only a girl in Harry's year left, just like Potters)
Currently led by Amelia Bones and Augusta Longbottom (major families)
Dumbledore (Counts and Voscounts, making a strong faction of his own)
Dark Alliance:
Nott
Lestrange (in prison, heiress being raised by Malfoy, with Narcissa as Regent, who is also regent of Blacks)
Carrows
Yaxley
Rosier
Parkinson
Flint
Bulstrode
Mort
Malfoy (are Counts but their cousins in France are Earl's and have a lot of sway in France so they are a major part of dark alliance)
Blacks (used to be a part but has grown closer to Light side since Grindelwald but sometimes reputation precedes them and Regulus was only heir at that time)
Currently led by Nott (Earl houses) and Malfoys lead Counts and Viscounts, so a strong part on his own equal to Nott.
Grey Alliance:
Greengrass
Slughorn
Crouch (will pass on to a cousin after Barty Crouch Sr.)
Avery
Selwyn
Burge
Gamp
McDougal
Rowle
Davies (Different from Tracey Davis)
Currently led by Greengrass