Matt,
I would wholeheartedly endorse Wordpress as well, it is what I use for the companies I work with as well as for my own. PHP based, with MySQL and ideally Apache 2 (for the fully SEO enabled permalinks).
The functionality is excellent and in addition you have access to a very powerful range of plug-ins from 3rd parties which will take it in any direction you care to choose from protecting against spam comments, to tags, stickies etc etc.
In terms of layout, my recommendation would be that you use the layout that you have on the rest of your site. I always think it is a little weird when I am on a website then appear to be transported to a set of pages which look totally different for the "blog" area with no way to get back to where I was! Choose a theme (template to you and me) that you like and then modify it to reflect your own site to integrate it properly.
Any issues, drop me a line.
All the best,
Mark