Notes.

I use 1) a calendar 2) a timeline 3) a list of names (including both assigned and unassigned names) 4) a relationship map 5) maps 6) a list of printed off monster & NPC stats and 7) a stack of index cards with treasure on them as my base. I then either write notes as short blurbs on each of these, or stick post-its to them, or in the case of the index cards, hand them out to PCs. I use a stack of blank index cards to write out NPC names and descriptions and to commemorate important events, and hand them out to the note-taker and the other NPCs.

The note-taker typically has a calendar (a different copy than the one I refer to), a stack of index cards with NPC names (or I've seen one guy grab an address book and list NPCs by name in it) and a stack of treasure cards.