Taking Notes: So far, the killer app for note taking is still OneNote, from Microsoft. Unfortunately, the boys from Redmond have not made the application available for any of the Apple devices, including the iPad. Absent that, I use Notes Plus, available from iTunes. It comes with a variety of useful features, most notably a way to zoom in for hand-writing and drawing. I've tried EverNote and PenUltimate, and this app easily betters them.
Instant Messaging: Meebo is an instant messaging application that will give you access to multiple I/M accounts at once. After setting up an account at their website, add log-in credentials for the various I/M tools you use, like G-Mail, Facebook, AIM, MSN Messenger, etc. I don't believe that you can set up a group chat across accounts, but that's it's only shortcoming. Well, that and the fact that the current version is not optimized for the iPad. (I just hit the 2x button to make it easier to see.( They have not announced when an iPad version will be released, though a lot of users have requested it.
Task Management: I have a lot of clients, and remembering deliverables and tasks for all of them is really challenging. So I use Remember the Milk to manage and organize my tasks. After signing up at their website ($25/year subscription), you can manage all kinds of tasks from the web site and from the app on an iPad, iPhone and even a Droid phone. Like Meebo, no iPad-optimized version is yet available, nor have they announced one for release. Even so, it does a great job helping me keep one synchronized list of tasks managed and organized.
WEB SITES FOR ALL THREE APPS:
Notes Plus
Meebo
Remember the Milk