WoD's Mage line has my favorite magic system of any RPG system. There are 10 Arcana representing different areas of magical influence (Fate, Force, Matter, Spirit, etc.) that you advance separately, and as you do so your power over that arcana grows. You also have a stat called Gnosis that represents your overall magical power (like Psy Rating in 40k). When you want to casst a spell, you literally just come up with whatever you want the spell to do (within the limits of your power -- a starting mage won't be stopping time or summoning armies of the dead) and roll dice to see how well it works. There are a number of example effects to choose from, but if you think up a cool new use for your power you can work with the GM to figure out the in-game effects.
That said, there would be some problems with porting such a free-form system to a crunch-heavy game like DH. A central theme in Mage is hubris, and some high-level effects really blur the line between mortal and god. A person with a single dot in Life magic can detect other life forms or interpret an animal's feeling, while a five-dot master of Life can transform their enemies into insects or create mythological creatures like dragons or manticores. A master of Fate can call down Biblical plagues of locusts, a master of Space can create their own (permanent) pocket dimensions, and a master of Matter can -- 100% literally -- turn military helicopters to Swiss cheese. DH Psykers are already crazy enough at high levels; Mage is a good starting point for designing a new power system, but directly copying it will not work in a DH setting.
EDIT: Here are the utility powers I'm currently considering for my game:
- Biomancy -- Alter the bodies of you and your fellow Acolytes to survive in extreme heat/cold, breathe underwater, withstand pressure from vacuum or deep ocean, etc.
- Divination -- This is the most utility-focused discipline in the game, so it doesn't need any help in this department.
- Pyromancy -- Use "precision pyromancy" as a melta-cutter, letting you cut through armored bulkheads... with your MIND!
- Telekinesis -- A super-strength version of Telekinesis that lets you lift very heavy loads, say 100kg per PR (the standard version is only 2kg per PR). Would only function on immobile objects and take an extended amount of time for the sake of balance.
- Telepathy -- Mind Probe ability that lets you conduct in-depth interrogations of a target, or the ability to plant a suggestion in a target's subconscious that will be triggered later (for example: "The next time you see the governor, shoot him").
Edited by Covered in Weasels, 17 June 2014 - 07:42 AM.