Viper is made by Directed Electronics Inc. They are the #1 mfg. in the world as far as these type of components go. IMO Viper is a very, very nice alarm system. The only drawback w/ DEI is that if you ever have a warranty claim they can somethimes be a little fussy. AFAIK Viper's are only supposed to be installed by an authorized dealer, but there are way around this. Just thought I'd let you know in case you were considering the install yourself.
I have a Code Alarm in my truck. It's a Sure Start LX. I am very happy with it. One nice thing about the Codes is if you every have some sort of warranty claim, they are very easy to deal with. There are some features of the Code Alarm that I like over the Viper and some on the Viper I like over the Code. Both are great alarms so whatever you decide is a matter of personal preference.
Alpine also makes very nice alarms.
There are the few that I have had expereince with. What is even more important than the Alarm itself is the installation. You probably don't want some hack cutting up wires under the dash of your truck. Best Buy and Circuit City may be some places to avoid. I'm sure there are some decent installers that are employed at some of them, but I bet most are not all that skilled. I would recommend you check w/ some of the high end car audio shops in your area. There installers are most likely a little more accustomed to doing alarm installations.
JMHO,
Ryan