microphone input jack for iPad?

None of the iPads come with a stereo input jack.

I do think the Apple dock connector has an input line. But I'm not sure if the iPad has an active line to it.

I'm not sure about the iPad, but I do know the dock connector (32 pin) on the older iPods at least do have an audio in line and are capable of recording in stereo. I don't know if they're still made, but there's a device called a "Mikey" which plugs into that connector on the bottom so you can record with it. I tried mine tonight on the iPad and it does NOT support that particular one. My Mikey is the very first one they made, without the USB port on the side of it, and designed for the very first iPod up to I believe iPod 2nd generation. The later design with USB port MIGHT work with the iPad. It was designed for later model iPods up to but not including those using a Lightning connector on the bottom. Mine records very good quality audio and I use it to record my own music gigs and playing and at open mic and full music sets I play sometimes.