Super Meat Boy - Ballad of the burning squirrel

Super Meat Boy - Forest Funk

Super Meat Boy - Betus Blues

The composer for Super Meat Boy has done lots of great tracks for Binding of Isaac and Crypt of the Necrodancer too (Danny Baranowsky)

Enter the Gungeon - Abbey or Die

Enter the Gungeon - Behold the Boss Eater

Enter the Gungeon - Boss Battle Beating

Metal Gear solid theme

Nine Sols - Collage

Hades soundtrack (all of it) + if you search for the composer (Darren Korb) then you'll find loads more great soundtracks he's done (notably for Bastion).

Hollow Knight soundtrack (all of it + the piano cover version)

Street Fighter 6 - Viator (theme for Ryu + there's a real cool metal cover that is on YouTube by an indie metal band)

Wipeout HD soundtrack (all of it)

Super Hexagon (all 3 tracks)

Hotline Miami soundtrack

Dead Cells

Lots of people have rightly mentioned FTL

Frank Kelpacki has done tons of great soundtracks across the whole Command and Conquer series and it's worth searching through.

If you're into chip tunes, then it is also worth checking out Streets of Rage 2 soundtrack.

In case you haven't noticed, I'm really into video game instrumentals. If anyone else is interested, there's a great podcast called Sound of Gaming by BBC radio 3 that is worth going through the back catalogue of episodes.