I've added Deleriad's suggestions to the blog.
Other suggestions very welcome. I'm working on a couple for Divine Casters.
For spirit magicians, how about:
Encorporate
Requirements: CHA 15+, Spirit Binding 90%+
Hero Points: 12
Duration: One task
Allows the Spirit Magician to give the spirit a corporeal form on a successful Spirit Binding roll. The spirit gains physical characteristics of the same range as its Intensity score (eg Intensity 1 get 1d6+6, Intensity 3 gets 1d6+18 - see S&P 89, p.14). Animal spirits will manifest as the appropriate animal. Plant spirits will be ambulatory. Bane spirits will manifest as a monstrous creature with a gaping maw and so on.
If the spirit is killed while Corporeal, it must succeed at a persistence roll or is lost forever. Most intelligent spirits will therefore need negotiating with to agree to Encorporation.
This ability would allow a magician with a bunch of Ancestor Spirits, for instance, to have them all appear at once, rather than only one of them possessing him.