I've always had difficulties doing anything but very basic edits with iPhoto. If you plan on doing anything, get Photoshop and Illustrator. 
there are major differences between a photo editor, photo manipulator, and a graphics program. I like iPhoto for doing simple things like adjusting contrast and color balance, cropping, rotating, etc. because it's simple to open and run on my mac. it's also a great tool for organizing photos.
illustrator, being a vector based program is great for creating graphics, such as my sig below, but for editing photographs (which are pixel based) it is not.
photoshop has features of all three types of software, I primarily use it if i'm in the mood for doing digital collages or heavy manipulation. also, i learned photography back in the good ol' days of kodachrome and darkrooms, and i like to treat photoshop as a digital darkroom of sorts.
then again, why am i telling you all this when i should be saying:
lovely portrait of mariana, tesh, regardless of how sideways it is.