If I was going to put my site for the public's use, what are some security issues that I should be worried about?
I know of SQL injections. What other hacks/injections should I be aware of?
It depends heavily on what kind of site you're putting up. Sites that deal with commerce and payment systems need to be more secure then a site detailing how to wash your cat.
In essence the more personal user interaction a site has, the more it's going to need to be checked for security vulnerabilities. A static html site will probably not have many issues while a site that allows people to register, purchase items, pay with a credit card online, etc, is going to need a much closer look at things under the hood.