The Antec 900 is a wide case and will provide sufficient clearance for any air cooler on the market. A sure bet if bucks are tight is the Coolermaster Hyper 212 Plus for around $35 US. If your wallet is fatter, go with the Noctua D14 for around $80, arguably one of the most effective air coolers available.
One other question that needs to be answered before you buy any cooler is the height of your ram. If the ram has a tall heat sinks then there might not be enough clearance between CPU cooler and ram if you go with the Noctua.