I understand if you are not interested in introducing your tot to the computer yet, but S caught me in a weak moment the other day and now there's no going back. Babygamer.com has a collection of links to a variety of free baby/toddler internet "games." They basically all work the same way - there is some type of response when any key on the keyboard is pushed. I have convinced myself that they are good lessons in cause and effect, but there are some that are more educational (i.e when a key is pushed the next letter of the alphabet comes up).
Also, we do not own an iPhone, but I have read/heard a lot of people talking about free and inexpensive applications for toddlers. One of my favorite blogs 1+1+1=1 has a list of a few.
If you know of any others, please feel free to comment.