Straight up ska (in addition to what other people have said): Streetlight Manifesto, Mad Caddies, The Interupters, Big D and the Kids Table, The Specials.

If you wanna go old school and to a couple of biggest influences on modern ska and way more punk: Choking Victim (later morphed into Leftover Crack) and Operation Ivy (morphed into Rancid).

Roots (like ska but a bit more chill): Stick Figure, The Expendables, Rebelution, Pacific Dub.

You may also like Sublime and the band made after that Sublime with Rome (although personally I don’t).

Also something not quite ska but kinda in the vein of, shameless plug for a great New Zealand band called Fly My Pretties.

Me First and The Gimme Gimmes do amazing ska covers of popular music.

Suburban Legends

Mighty Mighty Bosstones and Reel Big Fish are both classics. Im also a big fan of Madness. For Ska-Punk you cant beat Less Than Jake