In december, for a honeymoon with a semblance of romanticism, with plenty of sharks and blue water.... the south pacific:
Rangiroa, Tahiti or Beqa, Fiji
Best accomodation for honeymoon:
Kia Ora: water bungalows or private island with a few bungalows but on the other side of lagoon :
I also stayed at Le Relais de Josephine which was very nice but the gf liked Kia Ora accomodations. The food at Josephine was better to me.
Best sites:
Tiputa Passe (the only reason I remember this name is because I learnt to swear in french and spanish) 
AvaXXX Passe (sorry can't remember the name)
Diving:
Sharks: grey reef (loads and frisky too!), hammers (dec-feb) chasing eagle rays. There are ops who feed the fish including sharks to attract them.
Pelagic is also awesome but not much color in terms of soft coral. Current but that's why the sharks are there.
Sorry can't remember the dive ops I used... Blue something.
Beqa, Fiji
Best accomodation for honey mooners:
Lalati Resort: Nicer accomodations, more secluded and private.
Marlin Bay (name has changed now I think): More international menu, feeds you better, but more crowded.
Diving: Chummed shark dives with C. Leucas. Fat ones!
Soft coral is very nice, not as current driven as Tahiti.
Dive ops: Beqa Adventure Divers (BAD) or Aqua Trek Beqa.
I can't think of any other places with sharks that's romantic enough for a honey moon. I suppose the Bahamas is much cheaper but Stuart Cove type places are typically crowded (esp during winter time) and shark feed dives are boring to me anyhow.