I still have Unique Sampras dampeners from several years ago. I'm not sure but it's going on 10+ years.
The original Sampras dampener is the rubber cable grommet. I'm sure that's what he was using when he was younger. Then Unique started to market their version with his name on them. I've got both and don't mind too much switching between them depending on the frame.
I still have some in their package from when they came two black ones per pack. I bought them for 50 cents a pack on discount at a K-mart once.
On my current playing frames, I use a "black tennis ball" circle dampener that came with Wilson Ultra Wrap overgrip a few years ago. Black ones were packaged with pink and orange overgrip, yellow dampeners came with the black overgrip. The Wal-marts near me carried these packages. They dampen to the same level as the black Sampras dampener. I didn't care much for the yellow ones and figured they'd get dingy looking after at while.
When those were starting to disappear from the shelves, I bought a bunch of them to stock up. I like them because I haven't seen them anywhere else and they're less poseur-ey than the Sampras dampener when you use a PS85, kPS88, or black Wilson mid.
"The secret is to find your motivation every single time - your inner motivation - so I always want to improve myself..." - EV