I would say there are several good steakhouses in Carlsbad, but one of the newer and more interesting ones is at the Aviara Four Season's Argyle Steakhouse. It's certainly worth a visit! For a full review, see the following story:
By far, the Argyle Steakhouse at the Four Seasons Resort. Definitely #1, away from resort above the golf club house. The views were spectacular of the lagoon, and a great place to relax. Suprised to find the Argyle has a great bar, terrace, and regular seating. The service team relayed a recent renovation took place upgrading the interior by $2 million dollars, cool stuff by a famous Beverly Hills designer Cheryl Rowley. Our new favorite local Steakhouse in San Diego for sure!
Tommy V's is closed now. I agree with Roberta that The Argyle is great... but it is very pricey. For something still upscale, but not as expensive, try West. Also, another overall great restaurant is Savoury on El Camino Real (in Encinitas actually). It's French/California and the chef pairs all dishes with his wine suggestion (by the glass). I like!