WriteRight for iOS
WriteRight is an app for iPhone and iPad that probably won't replace your favorite iOS text editor (*cough* Editorial *cough*), but works nicely as a supplemental writing and editing tool.
It analyzes your writing and offers synonyms and antonyms for any highlighted text, and will even show alternative ways to phrase a multi-word selection. It understands gender, number, and conjugation, so its suggestions are usually accurate. The icing on the cake: these text-substitution tools work in both English and Spanish.
WriteRight will help spice up your writing, and there's no better time to try it out since it's on sale for $3, which is 30% off the normal price.