Another really cool language design is Korean hangul. The form of each letter represents how you put your mouth to vocalize it - among many nice features.
English has Shavian.
There's also Deseret, which I've made some tools for, but it's not featural (beyond some isolated cases, like ligatures for some-but-not-all diphthongs) and is somewhat confusing to learn.
Neither of these will be generally usable for the immediate future, since they're both in Unicode's astral planes, and some common piece of web framework (old versions of MySQL, IIRC) silently fails on encountering astral-plane characters. Font support is another issue, but Deseret is slightly better-supported than Shavian -- my Win8 install came with ...
I just read this in the Wikipedia article on the Mattaponi River and it really tickled me. If only all language were so rational!