Mine hands down will always be the March 14-15 2008 tornado outbreak because I had a very eerie similar experience as Trevor. (I found out two days later once we got power it touched down as a EF1 right around our neighborhood playground before heading to Downtown Atlanta) That next day I saw golfball sized hail for the first time ever. I knew we were in line for more severe weather that day, it was so hot and humid you would have mistaken the weather for June not March.
My second scariest is Hurricane Ivan in September 2004, it wasn't a hurricane when it got up here, but it was still a strong tropical storm and the only tropical system I have witnessed with lightning and thunder twice! Before Ivan, I never knew they produced lightning/thunder, only heavy rain/winds/tornadoes.