There are a lot of solutions available online to help with making notes and organising, and I've been trying out several over the last few months.
Allows multimedia notes to easily include pictures or audio, Catch also has a fully featured mobile and well designed tablet app which sync immediately with their website. Notes are can be put into separate "streams" which can be shared amongst other users or used to categorise your own notes.
The free version offers 70MB of space.
Remember the Milk
Possibly the most popular service here, RTM is primarily focused on managing to-do lists rather than notes, and has some fantastic integration into a number of social media services and calendars such as Google Calendar. They've recently added some rather smart Siri integration for iPhone 4S users, but their lack of an Android tablet app is frustrating.
Springpad offers both to-do lists and note-taking, but whilst the site is lovely, I'm not sure it presents either in a way that is helpful to me as some other services. There's a good browser extension to add any webpage to a note, and notes can also include images or audio.
Similar to Catch, Evernote allows taking and syncing multimedia notes across a huge number of platform (there are clients for Mac, PC, iPhone, Android, and web applications). Any note can belong to any one notebook, which can be shared amongst friends, or tagged to allow for more flexible categorisation.
Whist I'm not such a big fan of the Windows or Web UI, Evernote's tablet UI is my favourite of any of the services here - it's just a shame that it doesn't support to do lists.