MFM: Iambecomelife's Merchant Fleet Mod. Adds more that 70 new merchant classes to the game.
http://www.subsim.com/radioroom/showthread.php?t=170741
Flakmonkey's New Interiors. Adds everything but the torpedo rooms to the Type VII.
http://www.subsim.com/radioroom/showthread.php?t=162631
Both are very resource-intensive. With my old single-core rig I had to choose between them and the St. Nazaire mod. I like the working locks for the harbors and canals, so I made my choice in that direction.