Is there a mod that would show magic effects in the corners of the screen or something like that? I'm annoyed how many time do I have to click the inventory to see when my summon will vanish...

No, not yet. But schlangster, one of the people behind the SkyUI mod mentioned working on a framework that allows stuff to be added to the HUD, so i guess it'll happen sooner or later. I very much want one myself.

Edit: the deveploment thread: http://www.gamesas.com/topic/1386363-wipz-hud-widget-framework/