There are quite a few free GRx placefiles available, which will let you plot things like SPC products (watches, mesoscale discussions, convective outlooks, etc), surface observations (METARS -- ASOS/AWOS -- and various mesonets like the Oklahoma Mesonet, West Texas Mesonet, and so forth), and Skywarn / spotter-related repeaters, all on top (or beneath) the radar imagery. Speed and ease-of-use are next to none, and the dynamic placefile ability is one of the most valuable features. And hey, you can always make your own placefiles if you wish...
As others have said, Allisonhouse does provide lightning data for like $10/mo (includes a slew of placefiles and a reliable source for L3 radar data), and you can make your own lightning placefile if you have access to the data (I just finished up mine).
To bring this back on topic a little bit... I subscribed to WxTap.com back in the late-90s. I let the subscription expire when CoD picked up all 88Ds in the US (after the expiration of NIDS exclusivity), and I've been using GR software for the past couple of years (starting with the original sub-version 1 beta builds).
Allisonhouse has a free placefile feed, and I provide placefiles for free as well (see my
GRLevelX Placefiles page).
I wouldn't recommend anything but GRLevel3 (in the least, and GR2AE if you have the money) nowadays. This is not a shot at the other radar viewing applications or services. Rather, it's a testament to the quality of the GR program suite!