Boss Dr. Pad
The 3 versions of the Boss Dr. Pad devices were constructed as additional pads for drummers, but, of course, they're also great as effect sound pads. Besides 6 different samples, you get a wide scope of extensive functions, that can be operated via 6 real-time controls. These controls can generate interesting pitch and sweep effects, which again depend on velocity.
The open chip architecture allows some manipulation, making further interesting effects possible. I built a 5-switch matrix for beautiful noise effects into mine, so far.