Working with negative space and type.
I love the idea of layering different letters and playing with the negative and positive space, something I may take into account when producing my ten letterforms.
A more 3D approach... I think this is really interesting and worth experimenting with when developing my own work.
A great example of negative space used within an entire typeface, and other good typefaces to work with on his website http://damiankidd.co.uk/typefaces.html