Whiteboard
Push-Pin Board
Desktop File / Paper Tray (4 or so) to organize "IN", "COMPLETED", RECEIPTS, Packing Labels, archive mail/cc statements, etc... (whatever you find it useful for organizing if you don't have one alrady).
I keep numerous paper pads (yellow are my fav) as well as Stick-It notes around so I can write a quick note and stick it on the board as a visual reminder. Things are often lost on the PC/MAC for this purpose at-least for me.
If you don't have them already for ergonomics I suggest:
- Keyboard arm/tray (full adjustable one, not just a sliding in/out tray).
-- EgoStoreOnline.com I think they end up about $180 with the keyboard arm, and tray. Arm: V-AM17-11 & Tray: V-P05-11-S-F
- Quality adjustable chair
-- I like the Steelcase Leap
- Adjustable (angle) foot rest
Also, if you're adding multiple monitors to your single workstation I suggest calibrating them so they aren't varying darkness/tints so it's easier on the eyes. (This is often very hard if 1 monitor is really old.)