If you want to get a scanner for listening to AIR communications only, you don't need anything fancy (though it's nice to have extra features like weather and trunking for police/etc).
I just picked up a PRO-89 off eBay (~$40 + ship) and it works really well. Here is what I looked out for when I was buying:
* Reviews online are always helpful, such as eHam.net
* AIR frequencies are required (108-136MHz) - some don't have it!
* Portable... for me this meant handheld
* Power... I wanted an AC adapter included (w/ battery option)
Detachable/Removable antennas are pretty standard with the BNC connector.
If you're at the airport observing, you should be fine. If you're further away, an external antenna is recommended. There are many other threads on antennas. Goodluck and have fun!