Go to your local Mazda dealership. Both the Mazda CX7 and Mazdaspeed 3 antennas are stubbies, but not too stubby as to loose reception. They're an exact fit, which is nice, and are less than $13 Canadian.
Also, look up the shark fin, lots of people like those, even though I don't think it looks quite right on the hatch, being so far away from the rear of the car.
Another alternative is to pick up an antenna for the new RDX from your local Acura dealer. Exact fit, and people have gotten it for around $8. Here's a link to pics comparing the RDX vs. the CX-7 stubby:
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