Mighty Magick by DamarStiehl is a fun mod. To quote the modder:
This mod aims to make the "stock" spells of Oblivion more potent, useful and exciting...Currently, all magick combat in Oblivion consists of backpedaling while firing spell after spell into your opponent, or summoning creatures to do your dirty work. If you are sick of this, the mod is for you.
Additionally, a module in the mod changes the amounts of magicka each race receives, and alters the way Atronach, Mage and Apprentice birthsigns work.
MM isn't overpowered against magic users, because they get a boost to have more magicka than you've got. Against melee opponents it's another matter, but there's a nice, quiet joy in being able to blow an enemy running at you into the air just from a combination of force and game physics. Nor do the tweaks render you invincible, or even likely to kill off level 5 opponents with one blast--much less level 15, or 25. So, pretty well-balanced, and lots of fun, in my opinion.