Start with the JL Audio J2 amplifiers. Lots of honest power, low cost and a two year warranty provided you buy from an authorized dealer.
Next, look at the JL Audio G series as they're an exceptional sounding Class AB amplifier with a bulletproof protection circuit and two year warranty (authorized dealers only). Since they're in a model transition expect a 20 to 25 percent discount from legit dealers.
Btw, before summer is over JL will have highly effecient Class D XD series in 1, 2, 4, 5, & 6 channel models. Surprisingly inexpensive for a premium Class D,
good 2-ohm stability and awesome sound quality.

Earmark Marine