Maiar Spirits' Bodily Forms
 

Can Maiar spirits have more than one bodily form. When I say this I don't mean like differnent races or animals, but if its bodliy form is killed or destroyed can they create a new one automatically?

First, this has nothing to do with the creature being a "Maia" - the same will apply to Valar. "Maiar" and "Valar" are job descriptions, not races.

For all of the Ainur: Yes, in general. This does not apply to the wizards (in their time as wizards), Sauron, the balrogs, or Morgoth. In the case of the evil Ainur listed, they become tied to their physical body; in the case of the Istari, they agreed to become tied to their physical body. You should try reading the beginning of The Silmarillion. Ainur are not tied to physical bodies - they are (like you refer to them as) spirits, and can come in and out of physical shape as they wish.

Or the whole thing! It's great! :p ;)

One more thing to add: the Ainur who were capable of changing 'forms' generally did
so based on their mood, & chose their usual forms based on their individual dispositions (hence the fact that some Ainur are 'female' & some are 'male' - based on qualities generally associated with one gender or the other).

I've read all of the Silmarillion except the Akallbeth or however its spelt. It just wasn't very clear to me.

Actually, that subject pops up in the Akallabêth; when Sauron is taken to Númenor, he appeared to them in "fair visage," but after the destruction of Númenor (and Sauron's body with it), it is said: "But Sauron was not of mortal flesh, and though he was robbed now of that shape in which he had wrought so great an evil, so that he could never again appear fair to the eyes of Men, yet his spirit arose out of the deep and passed as a shadow and a black wind over the sea, and came back to Middle-earth and to Mordor that was his home. There he took up again his great Ring in Barad-dûr, and dwelt there, dark and silent, until he wrought himself a new guise, an image of malice and hatered made visible; and the Eye of Sauron the Terrible few could endure."