1.) Let's start with the most important product - the chair. A chair is a chair, right? Wrong! Ergonomic seating didn't start with the Aeron, but it did bring ergonomics into mainstream consciousness. There are a lot more ergonomic chairs than the Aeron - I personally like the Freedom from Humanscale, the Leap from Steelcase, the Chadwick from Knoll, and the lesser known sibling of the Aeron, the Mirra from Herman Miller. None of them are cheap (prices range from $518 to over $2,000 fully loaded), but these will save your back and rest of your body in the long run.
2.) Number two is a keyboard tray. There are several benefits of using a keyboard tray. Most importantly, they keep your arms and wrists in the most healthy, comfortable positions. Most keyboard trays are pretty straight forward to install, and they free up lots of desk space once reserved for the keyboard and your mouse. Humanscale and Workrite are the top two manufacturers in the keyboard tray space, and both have an extensive selection depending on your individual needs.
3.) Next up is a monitor arm...or for those lucky multiple monitor folks out there, monitor armS. Not only do monitor arms free up desk space, but they also allow you to position your monitor in a position that is comfortable for your neck. Your monitor should be slight below eye level. Not surprisingly, Humanscale, the ergonomic experts, also rule the field of monitor arms, but there are also great monitor arms from Workrite, Peerless, Chief, Ergotron and others.
4.) The fourth product is a lumbar support. If you don't have the best ergonomic chair, and can't fit one into the budget, you should at least consider a solid back support to maintain proper posture. Back supports tend to range from $20 to $100, so it won't break the bank!
5.) Last up is a footrest. From the Humanscale website: "Studies have shown that 70% of all women and 40% of all men have health issues such as blood clots, varicose veins and pressure on the Achilles tendon due to pooling of fluids in the lower limbs — the result of prolonged, inactive sitting." Wow - I don't currently have a footrest at my workstation, but that is pretty powerful information. I may have to pick one up. Like back supports, footrests are fairly inexpensive (prices are $30 to $150). Humanscale and Safco are the top two manufacturers of footrests for the work environment.
I'm off to the gym - something has to combat my "prolonged, inactive sitting"! I hope this information is helpful, and please feel free to shoot me any questions you may have.