For me it's GRLevel3 version 2 with the following separate add-ons:
PFQuery - A program that lets you display road names on the display by clicking on the road. It will also display certain weather info in text form as well. For example, if you click on lets say a 50dbz area of a thunderstorm it will put 50dbz as text on the screen.
Manual Storm Tracks - This add-on does just as the name implies. Manually makes storm tracks, and provides ETA estimates on the GRL3 screen.
SCIT processor - Displays and organizes storm cell info, and can provide audible alerts based on your warning preferences. For example, you can set it up to sound an audible alarm for any TVS signatures detected on your screen.
One piece of software that I've been using for years now, that isn't related to GRLevel3 in any way, is a program called WxWarning:http://www.wxspots.com/wxwarn.htm
This program sits quietly minimized to your system tray. It will sound an alarm (and pop-up if you wish) for a variety of conditions within the areas that you select. I have mine set up to alert me of any watches or warnings that occur within the state of Tennessee. Because I have this program is running on the system tray 24/7, it's usually the very first indication that I get that bad weather is moving into my area.
The program comes with two other real useful features.
1.) A user selectable pop-up tropical weather/mesoscale discussion window. Never miss another mesoscale discussion again with this handy feature! When a discussion is released, a pop-up window appears and an audible alarm will sound. Click on the link in the pop-up window and you will be taken to the NWS site where you can read the full text of the discussion.
2.) Graphical information. As seen in the picture above, you can display upto 12 windows of graphical information (jpegs, gifs, etc...) in one convenient place. Click on one of the thumbnails in the program, and you can see the image in full screen view. A very nice feature.
WxWarning is a perfect companion piece of software to any weather package you may be running.