Yes at this time there are three units out there, all three of them cost about 100.00 each and they can be found on Amazon.com. All three units work and work well. I'm a pilot and have used each of them and know people that use them as well.
Note all of them are WAAS enabled GPS receivers.
1. Bad Elf - This unit is different from the others as it plugs into the Ipad in the interfact/charge port. This means you don't have to charge it as it gets it power from the ipads battery. However as it attaches to the Ipad this may be a problem with most ipad mounts out there. Also it is easy to bump the unit and disconnect it. There has been a worry about bumping it and damaging the port but I have not heard of that ever happening.
2. GNS5870 - This is a small little blackbox GPS receiver. It has it's own battery that you have to remember to change and it interfaces with the Ipad by bluetooth. The only down side to this little guy is the one and off switch can be a pain in the butt untill you get use to it. Only work works with Apple products.
3. XGPS150 - Like the GNS 5870 this is a small battery power unit that needs to be rechanged. This one not only works with you apple products, but it would work with android or other PC's unlike the other two. You also get a couple of nice mounting options with this unit as well.
The XGPS150 is the unit that I tell people to get.