My recommendation is the SLP Loudmouth. Its loud and sounds outstanding. Also very easy to install and speedinc had a great deal on the price with free shipping just in case you decide on one.
Edit: There internet price lists for around 400$ however I called Speedinc and they sold it to me for around 370$ with free shipping, not sure if they were running some sort of special at the time but it wouldn't hurt calling it in anyway.