gallery – multiple image sizes

I am building my own theme, the website will feature my photography.

I would like to know if it is possible, or if there is a plug-in available, for building a gallery which contains mixed thumbnail and image sizes? At the moment I have been able to configure something that is based off 1 size, but when I want to add a different image size I have to setup another page for it… which is not really going to work as I will eventually end up with too many thumbnail pages – some having only 1 image in!

Thanks for any help, I am quite new to wordpress.

Elliot.