So the GURPS Bloggers voted on Powers that we use in campaigns. Christopher Rice went on to include magic systems as well. I play more than GM these days but I love to tinker so will include things I have planned for a campaign that hasn't run yet.
Affinity Magic
GURPS Magic is a solid system but is showing its age. I like the skills approach and the prerequisite system where you learn a basic spell before an advanced version. The limitations are the 2 page spell design rules for coming up with new spells and the college grouping of spells.
I decided to build one that had more flexibility, especially in spell groupings. This is based of Ritual magic (in GURPS Basic) and was submitted to Pyramid several years back but rejected. The initial version was more abstract to fit into an article but over time I found too many people complaining about abstract systems so I built a lengthy (almost 40 now) list of techniques that can be used to make spells.
The concept is pick an Affinity (spell grouping) and apply a given technique to create a spell. I have playtested it in two campaigns so far and am pretty happy with it.
Book/Path
I first saw this in GURPS Voodoo and like the concept but certain things kinda bug me about it. Recently I have been playing in a campaign that uses a highly modified version (Effect Shaping) and a friend has been wanting help converting Shadowrun/Earthdawn/Equinox to GURPS and three of us have bounced a lot of ideas around. These two things led me to outline a version I hope to pitch someday for publication. I use a lot of inspiration from Affinity Magic to create new Books and Paths and of course rituals. My current outline even includes such diverse lore as Cultivation, Tree Magic, Futhark Runes, Deaconic or hermetic Magic, and more that I will not be able to fit into one supplement.
Other Magic
I have used Sorcery, Ritual Path Magic, and some variations on those over the past few years.
Shamans
I like spirit magic and shamans in particular and it has bugged me that most RPGs treat shaman as pretty much any caster. Their magic lacks the interaction with spirits that I feel can make for good roleplaying. GURPS however has vast potential in this area and actually led to me writing for GURPS.
I have published some of my ideas for this and have at least 2 more in the works. Over the years my ideas have evolved somewhat as well.
Their are different kinds of shaman, but most can do an out of body experience (Trance or astral projection) and somehow communicate with spirits. So I built a set of systems allowing for different shamanic types.
Shamans have innate powers that they usually get from a near death experience and training. These include astral projection and the ability to see or talk with spirits.
Shaman then have external abilities that spirits lend them or represent actions spirits undertake on the shamans behalf.
Internal
Astral Projection, Channeling, and Medium each form the basis of a leveled power set. Astral Projection can build into the ability to create spirit forms, some of which are even physical. Medium is combined with Telecommunication. Channeling was the only one that was tricky but I decided it was learning to master ones Will and was able to create a leveled power for it.
External or Spirit Granted
I started off with Alternate Form as representing channeling a spirit in ones own body. This suits Voodoo and several other cultures and was done in GURPS 3e and 4e. I authored GURPS Powers: Totem and Nature Spirits to showcase this approach.
Medium represents talking to a spirit and persuading them to do something for the shaman. My current project GURPS Template Toolkit: Spirits was primarily designed to help a GM build a variety of spirits they can use to interact with shaman. Also works for horror and fantasy where you might have ghosts, nature spirits, or other things the party has to deal with.
Its too early to know what will make the final cut but I included some ideas for how spirits do magic themselves. Spirits can be Allies, Contacts, Patrons, or simply the special effect behind other powers, say Affliction and that will get more treatment in my last planned supplement of this topic.
Chimeric Powers
In my Chalice World setting I decided that most hybrid creatures were created by a trickster god. Chimera are hybrids of two or more races (centaurs, griffins, satyrs, etc.) but have an innate wild magic that lets them tap into powers based on their parent forms. This is mostly switchable advantages and Alternate Form but can go into other things too. Advanced practioners can even learn to tap that trickster chaos/wild magic they are born with to change into other hybrids and some other tricks as well.
Power Stunts
I never really got this until I read GURPS Psionic Powers but that one short section in GURPS Powers really has inspired most of my Powers as Magic builds (and I am not the only one!). Those rules are really what make Sorcery, Divine Favor, and other systems work. Alternative abilities, Character point powered abilities, Using Abilities at Default, Power Defenses, etc. all can be used to make for some very interesting builds and mini-systems.