Hey, grayshark95:
Since you are jailbroken (and mentioned you would like this ability) - I'll jump into this thread to tell you there is a Cydia app called Inspell that'll let you do this very thing. It won't autocorrect your miss-typings, but it will underline words it (1) doesn't have in the dictionary or (2) that are misspelled.
When you press once on the underlined word, you'll get a pop-up with some words offered as corrections. You'll also get an option (in that same pop-up) to add the word you typed to the dictionary.
You can also ignore the red underline or even set it up to autocorrect, just like the default.
It's very handy, very customizable and works in many apps (so far, I haven't found one it doesn't work in...). It also comes with the ability to add a toggle to SBSettings should you ever wish to turn it on/off.
IMNSHO, Inspell is awesome and is just the little helpful touch that Apple left out of the default spell-checker. It's $3.99 (USD) in Cydia. Worth every penny to me! Of course, YMMV.
Marilyn
P.S. Sorry I interrupted this thread, cause Inspell is for jailbroken iPads only ... just wanted people with JB iPads to know about this tweak.