I had this one installed a few months ago Clifford RSX 3.5
Got it from here SonicElectronix
It's all in one: alarm, remote starter, keyless entry. Works flawlessly. Very good range. Options galore and most of them either adjustable or can be turned on or off.
It comes with installation manual as well as options manual. I never looked into DIY though. I am not on friendly terms with electricity. Buddy of mine, who does this kind of stuff for a living, installed it for me. I was installing my CAI at the same time and had a chance to watch him work on my alarm. Was I glad I made a decision not to install it myself.
I tried it for a couple of weeks, just to see if I want any options changed. Went back to turn off "All Doors Lock With Ignition On" and to turn on "Unlock All Doors When Disarmed".
Oh BTW, my stock key buttons still work like a charm.

Hope this helps.