Where are you staying? We travel to the BI 2X a year and I've dove most of the sites. Your location and the waves are the determining factor on where you can dive.
My personal favorite is Two Step
south of Captain Cook and next to Pu’uhonua o Honaunau National Historical Park. I've seen everything Hawaii has to offer at the site but the biggest draw are the pod of dolphins that come in almost daily.http://www.shorediving.com/Earth/Hawaii ... /index.htm
If you're staying up north near the resorts Pukao
has two really good dive sites; Church and Village. I've seen several large Mantas at Church and village end is also really good.http://www.shorediving.com/Earth/Hawaii ... /index.htmhttp://www.shorediving.com/Earth/Hawaii ... /index.htm
If you are into sharks and getting the shit scared out of you, Alua Beach
near Honokohau Harbor (where most of the dive charters take off from). It's a bit of a hike with gear over lava rocks but the small beach is really cool and if you get to see Laverne it's definitely worth you time.http://www.shorediving.com/Earth/Hawaii ... /index.htm
A few other good sites:Mile marker 4
just south of Kona Town: http://www.shorediving.com/Earth/Hawaii ... /index.htmOld Kona Airport
in downtown Kona: http://www.shorediving.com/Earth/Hawaii ... /index.htmPebble Beach
on Kona Paradise(13 miles south of Captain Cook): http://www.divingkona.com/kona-paradise/Manta Dive
at the Sheraton: If your frugal (like me) and are up for a challenge this popular (expensive) boat dive can be done from shore. Let me know if you want to try it and I'll fill you in on the details.
A few tips....
Rent a small SUV or pick-up
. Some of the roads can be challenging for low clearance vehicles Jacks Dive Locker
is the best place to get tanks and weights. They have the best hours for pickup and drop-off of any of the shops in town
If you can, Bring or buy your lead: This is a weird one. I use 10lbs of lead for diving warm water. To rent the lead, it would have cost me ~$60 for 10 days. I asked them how much it would cost to buy two 5 lb blocks and the said $35. I ended up buying the lead and leaving it with a friend on the island.
If you have any questions feel free to ask.