I tried out this app called Speed Notes the other day (thanks to a mention on MetaFilter Projects). It's pretty simple, you tie the app to your Dropbox account, it creates a Notes directory, and then you can quickly create a new note by giving it a name. You get a blank document to fill with information at that point, which is pretty much exactly like the way the default iPhone notes application works.
The great thing about Speed Notes vs. Apple's Notes is that everything is on Dropbox and they are simple text files. This means they are instantly mirrored on every other computer you own. This also means you can make changes and additions to those text files from any other computer, and the information will be reflected on your iPhone.
I've found that in the last month or two of using Speed Notes I'm frequently starting notes and to-do lists as new items in the app while I'm out, and when I get back to my desktop computer, I end up modifying and fleshing out the files there, and I'm often looking back over the notes days later on my phone when I need them.
It's useful for grocery lists, to-do lists, travel information you need for a trip, etc. You can even share your notes directory with others to let them make modifications to the files too.
Overall, a great little app I didn't know I needed until I had it, and it's only $1.99. Totally worth every penny if you're a Dropbox user and fan.