1) One tool commonly used is the electronic version of Yellow Post-it® Software Notes from 3M.
This can be downloaded at: http://www.3m.com/market/office/postit/com_prod/psnotes/

You can use this digital version of the famous canary yellow® note to remind you to do something, to capture an idea or to organize all those important phone numbers -- all from your computer desktop.

2) Some people like a really a cool free online service called BackPack http://www.backpackit.com/
One important valuable aspect of the tool/service is the ability to setup reminders that are sent to you via a text message on your phone.In addition, others, such as your co-workers or your significant other, can add 'To-Do's' to your list for you.

Tens of thousands of people use Backpack to...
Organize to do lists, notes, images, and photos Plan a personal or business trip Keep track of what your competitors are doing Plan a home improvement project Collaborate on a new business idea Keep track of houses you're considering buying Gather information for a research project Keep a list of gift ideas for friends Build a For Sale page, Organize and plan a wedding etc..

3) There is another free tool called Evernote www.evernote.com. This tool allows you to create to-do lists and conveniently capture (drag/drop, type or web clip (via pgm extension)) and quickly find other typed or handwritten memos; excerpts from Web pages, emails and other documents; phone messages, brainstorms, sketches, snapshots; and more. It gives you a lot of flexibility in setting up categories.

4) Also, there is a tool called keynote notepad at http://www.tranglos.com/free/keynote.html.
It's freeware and it lets you enter single-click categories hierarchically.
That way you can have different categories for home, work, personal, misc. etc. You can also paste html, links, graphics and password protect them.