Since I have been using my iPhone I have only paid for about 4 apps. I think this has more to do with paying for something with out being able to try it first. Its like buying a house without stepping inside at all. Even with most apps just costing $.99 I still find it hard to just give my money away blindly. But for some reason I did that for the app TimeLapse (iTunes link). It does just what it says and takes pictures so you can make a time lapse movie.
There are all the options you should need to make a time lapse movies. You can pick the number of pictures to take from 1 to 9999. You can have it take the pictures as fast as it can (during my test it was about one every 8 to 10 seconds) and set the size of the photos from large to small.
Once you have your photos you can import them into iPhoto and use iMovie to make your time lapse movie such as the one below. Now this is a pretty simple app but it does just what it says and for $.99 its not bad. But if you are going to use this be sure to turn your sound off or your going to hear the camera sound over and over.