The most important thing about purchasing a scanner is to know what is in your area, system wise.
In other words- do any of the public service agencies in your area use trunked radio? If so, what type? (There are several types of Motorola systems plus EDACS, etc.) You also need to know what frequencies they are using for the trunked system- 400 MHz, 800 MHz, etc.
As far as standard comms are concerned- how big an area do you live in and how many "departments" do you want to tune in? I live in a county with 53 municipalities- one of the largest number in NJ- but my county is smaller than some cities in larger states. As a result, I only use about half of my 1000 channels in my scanner.
Digital- well, from some skimming the scanning message boards, it appears that digital will be an option on some new models of analog/trunking scanners. You purchase the basic scanner then add a digital board as an option (which effectively doubles the price of the scanner). Again- great thing if anyone you are interested in listening to is going to utilize digital transmissions- it ain't cheap for a municipality to install a trunking OR digital system. And there are still plenty of bugs. Additionally, I believe the first crop of digital scanners will only be able to handle 3600 baud systems, not 9600 baud. Again, you have to know what is in use in your area before committing the money, IMO.
Take my comments on digital scanning with a grain of salt and please, if I'm wrong, someone correct me...
... and, one last comment on digital- if the dept. doing the transmitting decides that they want to encrypt the transmissions, you're out of luck- no way to decode their encryption with current technology.
If you are involved with ARES/RACES in your area and have any kind of "in" with the departments you want to tune in, you can probably find out frequencies and system types from them. You may also want to post a message on some of the scanner groups on Yahoo Groups or similar email lists where someone can point you in the right direction for your area.
Additionally, check out some of the following web sites for more definitive information:http://www.trunkscanner.comhttp://www.cityfreq.com:81http://www.webdeals.net/k4lyp.htmhttp://marksscanners.home.att.net/index.htmlhttp://www.trunkedradio.net
Scanning is a fun part of the radio hobby and will add both more enjoyment to amateur radio, and more value to ARES/RACES/Skywarn emergency communications.
Good luck and 73!
Marlo Montanaro- KA2IRQ
Monmouth County ARES-RACES-Skywarn