So far the app store has been an amazing experience for me, and just about everything I've needed I've looked for and been able to find. However, there are two different apps that I have NOT encountered in the app store, so I am presenting them as ideas here for any developer who would like to take them up. If I had the time or ability to do this myself, I would, but I don't, so feel free to take these ideas and use them, if you are a developer and you are reading this. Keep in mind that whoever first creates one of these two apps will hold a monopoly in the app store on that app.
An Original Iphone FPS (first-person shooter)
This idea would probably require a development company (i.e., lots of resources), unlike my second idea, so if that is not something you have than I would recommend skipping this and reading the second idea. However, this idea has the greater potential to bring in large amounts of money. ;)
So, it would be a 3d game, first-person view shooter (obviously). The controls would be critical, though - and I've thought about this, and determined that the best way to handle it would be to have the aiming reticule controlled by the accelorometer, with a virtual on-screen analog stick to control movement in the bottom-left corner of the screen, and fire buttons etc. in the bottom-right corner. You would want online multiplayer with multiple-person matches and friend lists and a good single-player campaign mode with well designed levels, storyline, cutscenes, and bosses. That's about all for this idea.
A Music Composing Application for Iphone
Unlike my first idea, this one could easily be handled by a solo developer. However, you would still want to make it very cool. ;)
I often find myself composing music on the guitar, piano, trumpet etc., but I always end up not bothering to write it down (WAY too much effort - drawing out a musical staff and writing in the notes etc.). So I thought "Hey - an appstore app with a musical staff where you could just touch each spot on the staff to create a note would make composing so easy!", and went over to the appstore to see if such an app existed. Not the case. Someone should take advantage of this.
In the main editing mode, you would want to have a toolbar on the left hand side of the screen that would allow you to select what type of note or rest (or other sign) you're creating, and edit preferences like key signature, time signature, page #s, title and author, instrument etc. You would tap on the staff where you want to place a note (or rest etc.) to create one, and you could zoom in and out by pinching. You would also be able to select # of consecutive lines (to allow for composing for anything from trumpet to organ). Once you were done creating your piece, you could save it. There would be a category in the main menu that would allow you to browse saved pieces, and you would be able to select previously done pieces and either email them to your email address in full-on music sheet format (for printing and playing etc), or you could preview the piece by pressing a play button that would play your piece through the headphones for you using pre-determined instrument noises. I cannot emphasize how useful this app would be.
I am not claiming copyrights for either of these ideas, so they're up for grabs! Take them!