1) Aeron Chairs (or another comfy chair)
This chair is the first thing start-ups and entrepreneurs buy whenever they get funding, and they are well worth the higher price. As with the keyboards, most people in the office spend most of their day sitting down, and with the high level of customization built into the Aeron chair, it is the chair to get for the office.
2) A Mechanical Keyboard
Every SEO spends a ton of time typing, and a good keyboard can help. While mechanical keyboards are typically loud and sound like a typewriter, they are well worth the investment. So unless you work in an open office, I would highly recommend getting one. Das Keyboard and Razer make excellent mechanical keyboards with Cherry MX switches.
3) A stocked fridge and a table of
A stocked fridge with your favorite energy drinks, some beer and cokes just in case you have a late night programming session and need that boost of energy.
4) A Time Capsule (or another backup system)
If you have an Apple oriented office, then a time capsule will be the biggest time saver you will ever buy. The Time capsule doubles as a wireless router and backup system for all of the macs in the office, and will backup everyone’s computer every hour using delta updates (so it does not slow down the network).
5) Google Apps for Businesses
Every office needs a mail, office, and calendar suite, and while most businesses will go with Microsoft Office, Google Apps for Business gives a good alternative. Honestly, the Google Mail labs feature of “undo send” itself is worth the switch. Google Apps has a ton of features plus the ability to collaborate with your whole office using Google documents and Google Chat.