I personally love Ikea furniture. It's not the greatest quality, but it is a good price and good value. You can get the functional furniture you need for a fraction the price of higher-end furniture. The only catch is, the furniture tends to be harder to move around, so if you're planning on changing offices frequently, it may not work (moving around a room is not a big deal, but stairs and tight doorways can prove difficult once assembled).
If you can, I would visit one of their showrooms and see if anything strikes your fancy, and go with that. You can often get a more refined look if you see what options are available - much of their wooden furniture comes with a choice of finishes.
The one thing I would not skimp on though is the desk chairs. Considering how much time you spend sitting in it, make sure you find one that's ergonomically correct for you, and feels right. Test out a few before choosing one, and be aware that the cost of a higher-end chair more than pays for itself with savings from physiotherapy and massage therapy bills resulting from bad posture and a chair that doesn't really fit you.