Next in line for me has been MindNode ($5.99), which is also available on the iPhone and Mac desktop platforms. Its interface may actually be a little more intuitive than iThought's, and it only lacks a couple of export options (it handles MindNode format, as well as FreeMind, PNG, text outline and OPML outline). It auto-colors your branches, which can be handy when speed is of essence. Its overall aesthetic isn't quite as pleasing to me as iThoughtsHD, but it does the job well, and for a couple bucks less.
I would be remiss if I didn't mention iMindMap Mobile Pro from the father of mind mapping, Tony Buzan . It's iPhone-only right now, but it looks great on the iPad and is very intuitive to use. I'm not putting it at the top of the list only because it's not iPad-specific and doesn't play as nicely with the range of formats that iThoughts does, but it's a very slick app and makes beautiful maps. It has a "lightning" entry mode for very fast entry of ideas and thoughts. It's only $2.99, so it's definitely worth a look, especially if you want one app to use on both an iPhone and an iPad. I have fewer nice things to say about the desktop version of iMindMap, but that's a story for another time.
The last app I'll mention in this category is popplet lite. It's not, in my opinion, a fully-usable app yet, but it shows great potential. The main reason this version isn't fully satisfactory to me is simply that you only get one "map" to work with. Beyond that, it works like a loose concept map and is a really fast way to brainstorm with both pictures and images, connect ideas to each other and organize information. This lite version is free, and there's no "Pro" version, as of yet. I'm hoping the Pro version, when it arrives, will provide the few missing features that would make this a number one pick for me.
For me, brainstorming is both visual and textual. There are a few apps that do a great job of combining these modes, and Moodboard is definitely one of them. It comes in a free Lite version, and a $4.99 Pro version. I'm working with the Pro version -- some of the features I mention may not be available in the Lite version. Moodboard can insert pictures from your library or web captures using the built-in browser, overlay text and notes, and gives you a multi-touch way to quickly organize your "moodboard" by rotating, pinching and zooming, stacking and moving individual pieces. You can select from a pretty decent variety of backgrounds, and add arrows, text, tape and pushpins. It even has a palette tool built in that lets you build palettes from manually selected colors or by using a color picker on images in your moodboard. Export your Moodboards to your photo library, and share them via email, Facebook or Twitter. Overall, it's really fun to use and can be quite useful for gathering inspiration and brainstorming.
There's another app, Idea Boards, that does something similar, but I find it slightly less useful for my own purposes. If you prefer freeform and vector drawing and writing, though, this is one to check out. It's $1.99, and lets you combine line drawings, freehand drawings and scribblings and text in various colors and on various backgrounds. You can collect and manage boards, and each board has tabs so it can function as multiple pages. The drawing tools are rudimentary compared to something like Penultimate, but it allows typed text and other tools that make it more useful for some applications.
When it comes to simple note-taking, there's one obvious mention: Simplenote. Available for free on the iPad, it pretty much covers the bases for text-based notes and synchronization. Simplenote is available on the iPhone as well, and the Simplenote service plays well with several desktop applications. It's a go-to app for several TUAW bloggers.
There's one app that I'd been waiting for, though, and after excitedly downloading it and putting it to the test, I wasn't disappointed. It's called
Soundpaper Soundnote, and does for iPad note-taking what Pear Note and Transcriva do on the desktop: sync your typed text with recorded audio, allowing you to tap a note and hear what was going on when you took it. It's an amazing tool for taking notes in class and at meetings, letting you take half-baked notes which, when combined with the audio, allow for easy location of the actual information you were referring to. Taking the notes improves your information retention, and recording the audio means you'll actually know what you were talking about.
Those are my gems thus far. It's actually quite a satisfactory arsenal right now, but I'm looking forward to seeing these apps develop and new apps join the fray. If you've got some tips on your own favorite note-taking, brainstorming, information-gathering apps, please do let me know in the comments!