How come nobody suggested Midnight Commander as a file manager? It's my favorite by far.
You can use any file manager you want as long as its dependencies are installed. I have enough of KDE installed to use Konqueror, but I've never liked it. Thunar is the XFce default and I don't like it much, either. Of graphical file managers, I like xfe as well as anything.
Orage is a calendar. I wouldn't call it an organizer. I find it completely adequate as a calendar and I use jpilot with my Sony Clie PDA, and jpilot is all the organizer I need. It's got a calendar, address book, To-Do list, and memo pad. I'm pretty sure jpilot could serve as an organizer even if you don't have a Palm OS device to sync it with.
I don't like Fluxbox at all. I used IceWM for years while XFce was not very well developed. But XFce has become really good. Among the reasons I don't like Fluxbox and IceWM is that they are hard to configure. I don't like those text files. XFce is much easier to configure and customize.
All my computers have enough horsepower that I don't need to worry about how much RAM, etc., my desktop takes.