There are a lot of different products like that with endless rotary encoders. I build one myself from the midibox-project www.ucapps.de
But be warned, one major drawback is, that very few programms support full duplex midi-automation. That means when you automate your acid-line and want to change that automation later you have to re-record the complete automation again because the midi-controller doesn't get feedback. That's especially annoying if you want to use the controller to create synth patches. Only Ableton has very good support for that. Or you buy the Mackie C4 which is very very expensive
I just use a little m-audio midi controller keyboard, gives me 8 knobs and sliders to work with for automation, as well as a keyboard to fiddle with vst's. it was also very very inexpensive, but by no means cheap