Some time ago I posted some links, one of them pointing to a non-linear, graph like writing system called Ouwi; meanwhile I spent some time reading up on the topic of writing systems and have some more pointers:
Pinuyo is a pictorial language which indicates grammatical function of the ideograms by placement and surrounding symbols.
I also found a long, but sometimes deviating thread on 2-dimensional writing systems on the conlang mailing list archive. Unfortunatelly many of the links are now dead, the thread is from 2005.
Omniglot is a nice website about alphabets, writing systems and languages. It contains some constructed systems, like block script, a sylabic alphabet for the english language which combines letters to blocks (like the korean script for example). Most of them are linear ones.
I'm still wondering if there are some languages/alphabets optimized for reading speed. Most are either evolved, natural languages, which certainly are a compromise between reading and writing and the constructed ones optimized for speed like the morse code or shorthand.
In an edit, let me just add a few more links, somewhat related:
Láadan, a feminist language designed for countering male-centering of natural languages.
The gripping language, not spoken but transmitted by touching of the hands.