Version: 1.3.5.0

Equip a spell like flames, frostbite, sparks, ward, detect life or detect dead.
Look all the way down and cast it, keep on casting it until you run completely out of magicka BUT do not release the bumper!
Continue on casting the spell and aim at what you want...
You'll be able to cast the spell forever, even if you have depleted your amount of magicka. It works also with healing and clairvoyance.

I wonder if it's just my game or yours too... Let me know guys!

And happy holidays from Italy!

EDIT: works only in first person and only if you are casting a single spell or the same spell with both hands.

Very nice bug indeed! My particular favourite is, find a chair/bench to sit down on. Then, while seated, equip a torch in your left hand (remain in first person view). Then, look to your left. You will then see your arm floating high up. It looks like your arm is coming out of the side of your head! Obviously, the programmers have forgotten to reposition your arms when you sit down. Instead, they remain in the position as when you were standing up.

Haha! I've just tried out yours... Funny.
And the one I was talking about is well known? Did you hear about it before?

I've just tried repeating your 'infinite magical' bug but I can't reproduce it. As soon as my magica is depleated, the spell stops casting. I assume with your game, it continues to cast? I am also playing version 1.3.5.0

Try riding a horse with a torch equiped to set your groin on fire. No game tester rides horses at night?!

I've moved all my saves to a thumb drive and formatted the hdd. Then I installed Skyrim, restored my saves and the glitch is gone...
I guess it was just my game XD. Case solved.