Stay way from the cheep models (Bulldog's - had one, it worked for awhile but then range got worse and worse) I replaced mine with an ultra start you can find them on ebay cheep but if you try to get them through a dealer $150 and up. I have never had the Viper ones but have heard great things about them too, also Audiovox I have heard is good.
I think this is the model I bought
Ultra Start U1272-PRO I have gotten every bit of the 2,800 ft range out of mine. I did do the install on both of my systems myself it can be intimidating at first but its more of a pain in the butt job than hard. Getting to all the wires you need is the hardest part.
A couple of other things to think about is:
One way or Two way remotes - two way may seem like over kill but depending how you use yours it might be nice, if you can't see the truck from where you use it most.
(Original I bought the unit to have keyless entry, after I was married my truck went outside the remote starter, started getting used allot more but I could not see the truck from my bedroom, and when getting 3 kids ready in the morning running to check if it started became low priority.)
Make sure you get a unit with at least 1 button per function. (the Lock and Unlock need to be different buttons, other wise you are guessing what mode you are in, Bulldogs use 1 button)
Don't forget about security bypass modulus and make sure you get something that comes setup to work your door locks otherwise you might spend more on relays than the starter system.
Also save you instructions even if you have someone else install it. There are allot of programming things you can do. Make your lights flash, honk the horn when locking or unlocking. but if you ever change units to upgrade you will not need to rewire. Just compare the two units wiring diagrams and match up everything. I think I had my whole dash apart on the first unit I bought and it took me 6 or 7 hr to install. Cut that one out removed one dash panel and was done in 45min with the ultra start.
Lastly,
dolph comment on "put the keys in my pocket, it would start the vehicle." Choose the remote carefully for this reason. I drive one of our fire chiefs truck when he is out of town and it has an older model of the ultra start remote that kinda looks like a GM key remote but swear if you look at that remote the wrong way it will start the truck up. Only time I have had a problem with mine, is if I bend over and lean against some just the right way. I will say my bulldog remote was ugly to look at but it had a key protector and the buttons where the rubber type that were recessed in the remote. I never had any problems with that one, but that could have been b/c the range sucked on it too.