[jasondef]

Well, this question pops up a couple of times a week on this forum. I think the first thing is the JSGME mod enabler, this keeps your mod intallations organized and easy to install/uninstall/re-install.

Next would be SH3 Commander mod. Lets you tweak many more game settings, and adds color and features to you career.

After that I think the Harbor Traffic mod. Makes the campaign world much more interesting.

After that, it depends on what you want out of your game. More realism, of for the Real U-Boat mod (Rub) or the Improved U-Boat mod. There a continuous debate as to which one of these is better. Check the details of each and decide which is best for yourself what features sound good to your style.

There's tons of graphical and scenery enhancements, and numerous small little details that fix stock game bugs or shortcomings. And enhancements to the Nav map are essential, especially some of the tool packages when you start manual targetting.

One other little mod that I find real useful is the FABC Slideout mod, adds a quick access gauges slideout making it easier to check your u-boat's vitals.