Click the home button once to get to your iTouch's homescreen, then click it again. A search screen will appear allowing you to type in the name of the app you are looking for.
Here I've started typing in the app, Tan-Zen. After only typing in the first two letters, the app I'm looking for has already popped up in my search results. Just click on it in the list and the app will open.
Not only can you search for apps this way, but also videos, music, photos, and podcasts!
Now you can find that app FAST!