Forgive me if this sounds a little childish, but I was much younger when I came up with this one, and I really liked playing LOOM (old LucasArts game).
The magic system is based on an alphabet (probably not English, but I'll use it to illustrate). Your tool, be it staff, wand, sword, house, whatever, would be divided up into the letters A-Z. At first, you would only have access to a few letters, say A-E, but over time you would learn new letters and expand your 'vocabulary'. Spells would consist of a variable length of letters depending on complexity, number of targets, power of spells. More difficult and dangerous spells would contain higher letters, with possible earth-changing spells being up in the X-Z range. So far, pretty simple.
What makes it more interesting to me is that the letters are transferable, to a certain extent. For instance, if you had a staff with A-E, and you found another implement with F-I on it, you could graft them onto your existing staff and get instant access to those letters (although you still may not know any spellwords for those letters). Now, a given person may have really powerful letters, and weaker ones, based on how often they were used for spells (it could even be that certain letters were reserved for certain categories of spells—healing uses primarily vowels, attack magic uses hard consonants, defense uses word pairs like th and sm, etc.). So, you might find an old wizard's staff and discover that his K, M, and P were really strong, but most of his other letters were mediocre at best.
Building on that concept, there would come a point where a letter would be reclassified to artifact status. This being, it's really freakin' powerful. Any spells created with that implement using an artifact letter would have vastly superior capabilities. Trying to build an implement with as many artifact letters as possible has resulted in numerous wizard wars over time, with many murders to steal others' letters. There are lots of potential story arcs that I can think of with this, with the simplest being that a dire need has arisen for a really powerful complex spell (say, using Z), and the hero needs to find an artifact Z to complete the spell properly, even though his staff isn't even to M yet. He has to not only complete his staff to Y (in order to attach the artifact Z), AND find a letter Z powerful enough to use (which would be found only on ancient wizards or on implements that have been passed down through many generations), but the rest of the letters need to be powerful enough to complete the spellword, which he needs to learn as well.
Anyone want to drag this one into the dirt? I like criticism.