Yes. From <http://www.apple.com/ipad/specs/>:

  Input and output
    * Dock connector port
    * 3.5-mm stereo headphone jack
    * Built-in speaker
    * Microphone
    * Micro SIM card tray (Wi-Fi + 3G model only)

It's likely the headphone jack is even iPhone-compatible (accepts headsets with inline microphones), though the wording above isn't clear.