The above lists are all great so I won't try to duplicate and hit this from a different view..
Software..
OneNote: This has turned out to be the best campaign management software I think I have ever seen. (Can say enough how this has changed information management for my campaigns)
TableSmith: While not key, it is very handy to have especially if you get into making tables for world/campaign
NPC Designer: Never can have enough decent NPCs (Saves me hours in session prep and when I wing it)
Software..
OneNote: This has turned out to be the best campaign management software I think I have ever seen. (Can say enough how this has changed information management for my campaigns)
TableSmith: While not key, it is very handy to have especially if you get into making tables for world/campaign
NPC Designer: Never can have enough decent NPCs (Saves me hours in session prep and when I wing it)