I've got a new job and they offer a $500 work at home allowance. I've already got a good desk, good monitor, good general computer setup (I could probably use a better chair, but I don't think I want to spend for something extreme). Any other suggestions for what to use the funds on?
You said it already: On a better chair. This is the thing that keeps your body upright while you work all day in front of your computer. So like the tires on your car that keep you attached to the road, cheaping out is a not a good option. Unlike the tires of your car, a good chair is also a more long term investment. You don't want to have to replace it every year or two.
You mentioned having a good desk and computer setup. If you don’t already have an adjustable sit/stand desk and a split or ergo keyboard, I’d consider those as important as a good chair.
(PS: A good chair need not cost $1000. The Uplift Pursuit, Hon Ignition 2, and Uplift Vert are all totally reasonable and $300-$400.)