We just dived the Big Island the first two weeks of November 2011, and did a Manta Ray night dive with Kona Honu. We didn't get mantas, but the crew and boat were great, and we did a tour of the reef for a night dive instead.
We did shore dives at Puako and Two-Step/Place of refuge. Shorediving website was helpful, and I will add our dives there. The boulders and reef to the left of Two Step were fantastic, and the spinner dolphins in the bay at Two Step were great as well. There's also a few spotted eagle rays that hang out at Place of Refuge. Boat traffic was a bit of an issue at Place of Refuge. Over all, we preferred Puako, but both sites were fun and easy diving for two novices.