how would you like an ability system?

Normal learn ability
the one we all know and love from melee games.

Item ability
used in Imagica if anyone has played it. You purchase items and you are givin skills and abilities by that. i.e. you buy a speed orb, you get 3 abilities, invisible, windwalk, quik strike. Later on you can buy a higher level speed orb and get better abilities and maybe another skill.

Pre-determined
the player has no choice in what abilities he is going to learn for each level. It is predetermined in triggers and such. units is level 10, learn ability kill foe for unit.

which one would you like?

Mix and match; the more levels the hero has the better this works.

The hero (lets say Duran) starts off as a palladin. He comes with 2 spells: Holy light and divine shield, which he learns the normal way.
Lets say Duran reaches the city of Maia where he could buy Boots of Speed or Dragon's Fang. If he buys boots of speed he learns Wind Walk; if he buys Dragon's Fang he learns Breath of Fire.
Duran then helps a Dwarf in a side quest. He gives him Lightning Rune as a reward; the rune gives Duran the spell Storm Bolt.
At level 10 Duran learns Devotion Aura and at level 20 he learns Ressurection.
Also if Duran goes to the Dojo he could gain the ability to learn Battle Cry; Battle Cry apperas on his Research Card.

Would buying spells from shops and gaining the abilities instantly be considered items?

the best non-standart system is the spellcraft way: you buy different kinds of items, and forge a spell out of it. Aside from that, i prefer the standart system

Though how would you make it so that the spell can be learned?

You buy item. When you ues the item a trigger detects it and gives ability. Item does nothing.

spellbook, my spellbook I like that method most.
http://www.wc3campaigns.com/showthread.php?t=53832

I like the idea of item-attached abilities - it allows good versatility/options for heroes, rather than having pre-defined heroes.

Weebabe, don't sabotage people's threads.

however, making all these skills avaible to a hero can screw up every game, when ppl combine skills like divine shield, shadow strike, banishment, stormhammer and life drain together :<

Not necesarily. It depends on what types of spells you have available to be bought.
For instance you could only buy damage spells, like breath of fire and chain lightning.

And/Or only certain classes/races can buy certain spells. For example only warlocks and mages can buy advanced battle magic (eg earthquake) while only Tauren can buy Reincanation.

Spellbooks are good as you can have lots of spells but its weakness it that you cant hot key the spells, only the spell book (i think).

Thats where my spellbook comes in. It allows you to move spells from it into your command card. I'm still looking into fixing some its quirks. (Not being able to remove spells, only being able to queue them out, and when a spell is coolingdown you can't remove it meaning your spellbook is quite useless for 180 seconds after you cast avatar.)

check out vexorian's engineering upgrade test... i like that for a spell system