I'd look out for Cabelas' sale on their AGM batteries. They go on sale and combined with free to cheap shipping deals, you can get a great battery AND shipped.
From what i've seen, Cabelas usually discounts the batteries around $30-50 each on their sales.
Sears Odyssey AGM's have good regard as do Deka AGMs, and Lifeline AGM's.
In general, i think AGM's over flooded wet cell are better for boats. You'd get more bang for your buck with wet cells if you make sure they always have adequate water levels and are kept charged up, but too often we don't check or monitor them enough to get the max life from wet cells IMO (i MAY check mine once a year only! when they die will switch to AGMs). AGM's by design are generally more robust in construction more suitable for bouncy boat conditions and require much less maintenance, have a much slower rate of discharge when idle, no fluids to spill or fill, can be mounted sideways, but are generally more expensive than wet cells, but should last longer than a wet cell since they don't require much if any maintenace other than charging.