if you are looking on oahu, hicentral.com is the official site supposedly. there is also a rental section as well. my last place that i lived, i found through that site. if you are buying a property, use these links below. you can find out the current owner, flood zone information, building permits, and a lot more. very good research tool.
if you are looking for a great site check out oahure.com. it's probably the most comprehensive database information that i've seen. real simple and basic, so a caveman could do it. lol. they have email updates, so it's pretty cool. their historic data is pretty good as well. but we used their realtor for our purchase. not the greatest since she is busy, but she did setup a bunch of appts. also you do get 20% off their commission, and i can verify that they do it.