Oblivion Spell Question

I am really low ranking in my spell department. I need to cast shield spells to boost the attribute that governs them (cant recall offhand what it is).

Where can I get a shield spell that doesnt require a 25 level of magic?

Also, what are some essential spells to have? I already have healing, fire, and lightning. It seems to me that a lot of the spells are worthless.

depends on your race/class. if you're a melee fighting character heal is all you need

My charactor got caught stealing from The Wizard Guild at level 5 so if he needed any magic items it meant trips through the many dungeons, visits to the gates of Hell-Mart, or just hacking a shop owner to pieces. It's been so long sinceI beat that game I highly recomend taking the Assassin's Guild quest as it leads to becoming a vampire and your final mission is AWESOME