The only one I ended up downloading was the Wi-Fi Finder app thinking it might be useful for traveling this summer. I don't have a data plan for my iPad, so it might be handy to be able to find wifi while I'm offline. I did a couple of searches and it works! It's cool that it shows it on a map.
One not listed that I frequently use is called Sleep Cycle. My boyfriend who is an airline pilot recommended it to me. Supposedly it monitors your stage in the sleep cycle and awakens you when you are in your lightest sleep state. I can't speak to its scientific credibility, but I am waking up feeling less like a zombie. The wake up sound is a soothing music that gradually gets louder.
To use it, you set a half-hour range of time for when you want to wake up. Then you make sure it's plugged in and it's resting face down on your bed. It probably won't work as well if you share a bed, but according to the pilots who use it while staying in hotels, it makes a 3am wake-up much more pleasant than being jarred awake by a noisy alarm.