The Hackmaster Magic system is currently being rebuilt from scratch. Until then, I suggest that you continue to use the 2D&D magic system, with the modifications already included in skills and abilities.
The Hackmaster magic system borrows spells mostly from 2D&D (mostly), but reorganizes them. All spells in Hackmaster are assigned a relative `level' of power called a circle (to distinguish it from character level) from the lowest (0) to the highest (9). Characters gain access not to individual spells, but instead to Domains of magic. A Domain is 10 related spells, one spell of each circle.
Domains are a nifty idea. Are they actuall worthwhile? Are they too scary to new players? Their main effect is to limit the number of spells in circulation in the game (once you have the `Fire Domain', then there are only 10 spells to worry about). The downside to this is that either you're limiting the versatility of magic a lot (quite possibly a goal), or you're going to end up with lots of very similar domains (``Area Fire Damage Domain'' versus ``Single Target Fire Damage Domain'' versus ``Utility Fire Domain''). Right now I want Hackmaster to use the mixture of improvisational/dynamic magic and Spells/Rotes similiar to what's used in Mage and GURPS/ch4. As usual, GURPS has some nice details, but is too complex for my taste. Instead, I'm going to use a set of areas similiar to Mage, (continue to) add in magical skills for impromptu use, and start making a list of known spells from these groups. For starters, I could use the 2D&D grouping instead of my own, but I think I'll like the results better this way (not a big deal, since they will be `gone' in 2D&D).
Mage: correspondence entropy forces life matter mind prime spirit time
GURPS:
Animal
Body Control
Communication and Empathy
Elemental Air
Elemental Earth
Elemental Fire
Elemental Water
Enchantment
Food
Healing
Illusion and Creation
Knowledge
Light and Darkness
Making and Breaking
Meta-Spell
Mind Control
Movement
Necromantic
Plant
Protection and Warning
Sound
Gate
Consider spells-as-skills, domains-as-skills, and spellslots-for-sale.
Everyone has the innate potential to use magic (disad: no casting, no magic, antimagic). There is one kind of magic (no divine or arcane distinction). By default, characters have a number of spellpoints equal to their level. 0-level spells almost anyone can get; higher-level spells require more study (cp). Characters can buy spellpoints (limit?) or maybe spell slots, as well as skill/ability in spellcasting (spelllevel, spellcost, spellweaving).
Issues: