On my travels yesterday I discovered that the MTA has launched a new ten-trip Airtrain card. Previously, one had to pay $5 every time the Airtrain station was transited.
The new 10-trip card costs $25 thus providing a 50% discount per transit. This is great for people who travel to and from JFK regularly. The card I bought yesterday is good until July 2011 so there doesn't appear to be a "short" window for usability either.
Now if only the people at NJ Transit would do the same for EWR...
ETA: It appears this has been around for a while though not very commonly known. So, I stand corrected on it being new, but it is still a neat thing for those who don't know about it.