Roland TR 909
Roland TR 808
Roland TB 303 (pure sex!)
I wish I had any of those. I have a Roland TR-505, which sounds good (especially for using 12-bit samples), but is pretty far from being user-friendly.
I'm also not a fan of using knobs to set the tempo. If you're trying to do something exact, after a while, the tempo will usually shift one beat either up or down, and while it's not noticeable on its own, it can really make things weird if you're working with loops.