It's so easy to buy stuff for the iPhone, too easy for a sucker like me. Most of my purchases have been ill-thought out and somewhat rash. Many have been used for a few days and then unceremoniously dumped shortly after.
Listomni Lists however should last the pace. This cost me £3.99 and has to be great value. It reminds me of ListPro and is the nearest to this I have found yet. I like it because it is more fully featured than most list style software I have tried so far, Zenbe Lists, for example, is good but a bit basic although it is free and for many will be good enough.
-Quick data entry
-Never type an item twice
-Group and Sort List items the ways you want
-Switch quickly between different views of your data NEW!
-Email whole lists, or just a few list items at a time.
-Move lists between iPhones running Listomni NEW!
-Create as many lists as you want
-Organize lists in folders
-Customize the tab bar for quick access to your most used lists.
-Check items off lists to get them out of your way
-Protect your lists with a combination lock NEW!
-Fully Illustrated Searchable Help. NEW!
-Shows the number of unchecked items in each list and in the app. NEW!
-Create any number of dictionaries to autofill different lists. NEW!
-Protect your data offline easily with Backups NEW!
It allows you to set up various types of lists and has folder support. So for example, one of my main lists is titled "iPhone" on the main screen but it has different "categories" inside for different things. There is a built in ToDo manager and Shopping List, each with their own dedicated hardware access button for easy adding of items. These mini icons at the bottom of the screen can be changed to include your most oft used Lists/Folders. So far, I have found this to be a better List/Todo organiser than my previous favourite, Things for several reasons, ease of use being one. You can also backup by sending yourself an email with the backup file attached.
There's also a fairly comprehensive built in Help Menu for quick on iPhone reference.