I don´t dive (problems equalising) so can´t really recommend a specific diving company..... they all have good records here on the island from what I have seen and I am sure if you emailed them directly, they would come back you pretty quickly.... most companies are pretty communicative.
There are a number of excursion companies running too, it depends on what you are looking for. Family fun day out, glass bottom boat, more of a "party" boat, sailing boat etc.....
Quite a few places also hire out kayaks which is a great way to explore too.
Yes the forum will be great, just needs more entries, but I guess thats the way with everything. There are so many ways to share information these days, its the collating it that can be the difficult thing