I personally had used many times jQuery prettyPhoto plugin for my HTML sites. It’s the best for me. Now I found the same plugin for wordpress. Very easy WP-prettyPhoto.
In a default state, any image you’ll put in a post or page, will be elevated with a lightbox, if you add a link to another (larger) image before it. But of cause many custom options are available 😉
Check my example here.
P.S. This plugin doesn’t work with Syntax Highlighter ComPress