The Scorpio alarms seem to be good plug & play units. No wire cutting with their OEM connector kits. They aren't cheap: Scorpio Motorcycle Alarms
+1 for scorpio. I have the i900 with pager and I like it alot. Definately get the OEM factory harness for easier installation - like tibadoe say, plug and play. I also have the accessory ignition disable with the alarm but have not installed it yet - gonna have an indy do that because it involves splicing into wires.
If you have the HD security system on your bike I would buy the HD security siren. It's plug and play. Took me 20 minutes to hook up. I paid like $80 for it. If you decide later to add the pager it is very easy to sink with your security siren.