After estimating the height I needed to raise my desk, I bought some cinder blocks and pavers from Home Depot for about $10 and just put them under my desk legs. I used some old books to prop up my monitors, but blocks of printer paper work well too.

An anti-fatigue mat is an excellent investment, but even with that be prepared for a few weeks of achy feet/legs. You get used to it eventually, but man, it feels nice to crash on the couch in the evening.