Looks like a nine speed. Shimano or sram will work well. As an aside, a campy drivetrain (shifters AND deraileurs) will shift a 9s "S" brand cassette just fine. At least it does on my bike with this setup. Just be sure to pick up a 9 speed chain as well.

Any "hyperglide" lockring tool will work.

To fully take this home: this wheel has 130mm OLD spacing and will take 8/9/10 speed cassettes, and a 7 speed with a spacer to fill in the gap left by the missing cog.