2010 Pinpoint Lightning is probably the app you're looking for. It keeps you up to date on where lightning strikes. I think it's actually the only app that does this.
Also if you are looking for the most comprehensive weather map and are looking for a serious product, go for Radarscope. During tornado season in Oklahoma, I use a combination of Radarscope and MyCast Weather to supplement my chasing needs Someone also mentioned WVEC radar which is a great free solution as well.
For Radar on my phone I am a fan of RadarScope. Aside from Angry Birds, it's been the app I have most gotten my money out of. When in my work car, I normally use the NWS radar on the Toughbook, but RadarScope comes in handy in being able to place my GPS location within the storm path.