Continuing into my other most useful apps (but not ones I need every day) …
- WordWeb is the best dictionary app I've found for offline use. It also has nifty tools for word puzzles such as crosswords. I think it was free.
- it's more than possible to read Wikipedia in a regular browser, but Wikiamo is a purpose-built app which is better designed for a small screen, and has some other added benefits. But if you use an iPad, then I suggest Wikipanion has a more appropriate interface.
- TreeID was an impulse purchase when walking through fields with the in-laws, and we wondered what a particular tree was. Having just bought the iPhone I muttered "I bet there's an app for that", and then discovered there was. It's not fully comprehensive, but quite fun all the same.
- WhatTheFont is also definitely in the fun camp. Being a font geek sometimes you just need to know what a particular font is: with this app you take a picture of some text, type in the letters it represents, and then a minute later you have the best guesses from the website of the same name. Almost magic.