The beach resort of Pattaya is about 190 kilometers from Bangkok, making it the closest place to the big city, and its big airport, where you can find some diving. I'm told the diving here is not as good as other places in Thailand, but it does seem to have the highest density of potential wreck dive sites, if you're into that sort of thing, or want to be.
Pattaya's rather idyllic beaches first started attracting visitors in the 1950s. Later, it became very popular as an "R & R" destination for American servicemen during the Vietnam war. This beget a rather sleazy "industry" to service the servicemen, if you'll pardon the expression. Pattaya is still trying to shake off that image, with only limited success.
Still, the area does boast several nice hotels in every price range, as well as many good restaurants to try, and you can easily avoid the more honky-tonk side of town. See the full Pattaya travel guide at ThailandForVisitors.com for all the details.
The dive destinations around Pattaya can be divided into three areas:
For a good resource on the airea dive sites, visit Pattaya-Scuba.net.