Speculah:Magical Powers
From what we could see, magical girls have two kinds of magic power - material (relies on gem power to create items) and supportive (might not use gem power at all, greatly affected by wish).
Material magic
This one allows to create various things using gem's power. It's also possible that if created item is not returned back, gem gets dimmer, otherwise remaining at same level. We saw many applications of this magic already - it's magical girl costume, all the weapons they create, binoculars Kyouko used, possibly her food too.
Supportive magic
This one consists of few skills every girl can use, but power of each skill heavily depends on wish.
Healing
We saw Mami and Sayaka using it. Mami used it outside battle and took some time to heal minor wounds on Kyuubey, while Sayaka used it in battle to fully recover from major damage Kyouko inflicted. This one was explained by Kyuubey - her wish made her healing abilities really strong.
Bind/Barrier
This one was specialty of Mami, but Homura used it a bit in Prologue too. Mami's proficiency in it leaves a question - what kind of wish could affect it so much? "I wish I fastened my seatbelt" is hardly correct answer.
Time stop/Time bubble (unconfirmed)
Seen twice in ep.5. First, Sayaka uses it for few seconds to stop Kyouko's spear with a sword (that's first time we see water drops hanging in the air). Then Homura uses greatly advanced version of it - she leaves message to Madoka and then saves Sayaka, also giving her some time to rest (note how Sayaka is laying when Kyouko is about to strike, and how she's resting behind after Kyouko lands). Although full time stop does leave some major inconsistencies (Homura could use it while hunting Kyuubey and escaping Mami's bind), Time bubble (where time keeps flowing not personally for caster, but in some area of simple form, which can't be left without resuming time) explains most things. Is Homura is really proficient in this, it makes her wish heavily related to time, which supports time loop theory.
Teleport/Blink (unconfirmed)
Alternate vision of Homura's skill. Time manipulation version does not explai Homura's appearing out of nowhere after being hit by buiding in prologue as well as some of her movements during Charlotte fight. She might have both abilities, which leads to even more powerful wish.