ZBrush modeling app
I happened upon a reference to ZBrush in an interview with Tim Sweeney so I Googled it up and was duly impressed.
Traditionalist 4-panel modelers may be put off at first but I highly recommend checking out the demo videos. There were several "holy crap" moments for me in the first video. Granted, I haven't kept up with the latest and greatest high-dollar commercial apps, so your mileage may vary. It's not too expensive, either - $489, Win or Mac.
ZBrush is looking pretty cool. I messed with the 1.51 demo, and the interface is pretty complex and takes some getting used to. It is being used for a lot of organic hi-poly modeling nowadays (Doom 3, Unreal 3, LOTR, etc.) For fine organic details and doing things like normal maps nothing beats it.
I have Zbrush 2. It's an amazing program, but the learning curve is high. Thankfully though the community is very strong, and the tutorials are everywhere. Also, Pixologic have a habbit of releasing free updates (the next one looks amazing) and really giving you your monies worth. A great program, but not everybody's cup of tea. There are lots of other ways (and programs) to produce highly detailed normal maps.