Aftermarket isnt as difficult as some might think if you have the right parts
This is the module your going to need
http://ifar.ca/en/products/evo/evo-chr/
It covers all lx years including the new style key. Only requires one key to program. Its also one of the easy and fastest one I have install. The only parts a pain in the ass is getting the key cylinder out on the 05-07.
As for remote starters, I have had good luck using anything audiovox makes either prestige or code alarm brand. We just started carrying crimestopper. They didnt have a very good reputation a while ago but they them to make a nice turn around.
I just recently installed crimestoppers 2 way touch screen alarm/remote starter in my car. and so far I like it I would change a few of the button layouts.
prestige
http://amdistributors.com/mobile-catalog/summer2008/Audiovox%20Security%2018.pdf
code alarm
http://amdistributors.com/mobile-catalog/summer2008/Codealarm-Flashlogic%2019.pdf
crimestopper
http://www.crimestopper.com/2009/main.htm
here is what I install in my car
the module is 90% just plug and play. There is only a total of 5 wires that have to be wire in with your factory wiring

All wired up ready to get installed in the car.

The remotes

Close up of the touch remote

Im not sure about all the vendor/ selling good rules. But I can get anyone anything alarm/remote start related as cheap if not cheaper than any shop around.