Wavesurfer will work with any National Instruments X-series board. (These have model numbers of the form "63xx".) If you're interested in running real-time control loops, we recommend that you get a PCIe board (not USB). Which board you buy will depend on your specific needs, but if forced to give a recommendation with no more information, the PCIe-6341 is usually a good choice. When used with WaveSurfer, it supports up to 8 analog input channels, and up to 2 analog output channels. For a typical elecrophysiology rig, you probably want to get it with a rack-mountable BNC-2090A breakout box, instead of the default SCB-68A breakout boxes. An example "quote" is here, generated on June 9, 2016.
If you need more than 8 analog input channels, or more than 2 analog output channels, or think you might in the future, then we recommend the PCIe-6353 card, which supports up to 16 analog input channels, and up to 4 analog output channels. This requires two BNC-2090A breakout boxes. An example "quote" for the 6353 is here, also generated on June 9, 2016.
updated June 9, 2016