It's interesting that Wikipedia says it's pronounced " S-Q-L" but was historically pronounced "sequel."

Also interesting, MySQL says on their site:

The official way to pronounce “MySQL” is “My Ess Que Ell” (not “my sequel”), but we do not mind if you pronounce it as “my sequel” or in some other localized way.

Lastly, for those curious, PostgreSQL says on their site:

PostgreSQL is pronounced Post-Gres-Q-L.