Check this link:
http://en.wikipedia.org/wiki/OBD-II_PIDs
It has tables that show what data is reported. Obviously, different readers have different capabilities to read what the bus is providing.
The cheaper OBD-II scanners won't read what the dealer scanners will (at least that is what the word on the street is).
Harbour Freight has them for under $50 bucks and Wal-Mart carries one that goes for $98.00 which looks like a better item than the cheaper HF model.
HF does have a range of scanners tho, so you can get what your wallet will cover.
You can find them online at Amazon.com, or your local AutoZone or Snap-On, MAC Tools, Sears, etc. Not hard to find, just pick based on price and capabilities.
As for the wi-fi versions, not sure if the cycles per second rate of information transfer will be what you are looking for as they are not "real time" per se.
Kind of like the TPMS sensors on your wheels, they report about every 50 seconds or so, so if you're trying to rely on that timing cycle, you're not going to find it very useful.