thinksync.com.au

We've used K2 on a number of projects, but our own corporate site has just seen a re-working with K2.
Some notable features:

Several different K2 templates
Created a case study/portfolio system using K2
Integrated Simple Gallery Pro as part of the portfolio (wish there was a way to link the article image with the gallery so users could just click 'next' and 'prev' as if all images were grouped)
Integrated Disqus - without the K2 plugin. Just used the raw Disqus code and inserted into the templates where needed. Much more precise, particularly when you want to control the categories its used on
Integrated the AddThis plugin with custom icons - again, could have used a plugin, but I really wanted more control over placement, so I did it in the templates
In a lot of cases (but not all, will have to keep working on this) I've stripped back the template code entirely to only have the options I want available - that way anyone else posting here can't screw it up
I've used a free, licensed-for-web @font-face font, ChunkFive to have cross-browser live fancy fonts
The site itself uses progressive enhancement - CSS3 techniques used sparingly. Nice browsers see shadows, letterpress, rounded corners... crap browsers get less...

I've still got more work to do to get it completely up to scratch, but it's getting there!