Coming up with good ideas is a major part of your job, so you want to have the right tools on hand to generate as many ideas as possible during a brainstorming session. Here are some tools and techniques for doing just that.
When you want to do free-form thinking and gather ideas and tasks around a central concept, try a mind map. In the middle of the page, write down your topic. Then, all around the topic, jot down tasks, words, ideas, and connect them by drawing lines between them and branching similar ideas off of them. The most effective offline tool for mind mapping is probably a classic whiteboard, wet marker, and eraser. To mind map online, check out MindMeister.com, a free Web app where you can create, share, and publish your maps. The advantage of mind mapping is that it's not linear bullet points, and because it's unstructured it can encourage more free thinking.
Sometimes all you want to do is generate a bulleted list or outline of your ideas as they come to you. The low-tech solution is lined paper and a good pen, but if you want the ability to easily rearrange the items on your list or outline, you'll want some sort of outliner program. Microsoft Word's built in outline view is an easy way to make bulleted lists. In Word, press Ctrl+Alt+O to switch to Outline view.
When you can help it, don't brainstorm alone. The more people involved in your brainstorming session, the more ideas you'll generate, and the better your chances for finding the right idea will be. Pull key people together either in an on-site or virtual brainstorming session, and go to town. Allow for bad ideas to come out and stand to create the possibility of spurring on better alternatives. MindMeister supports collaborative mind maps--you can share maps you make there with collaborators. Google Docs offers excellent collaborative features like live-typing, where several people can be brainstorming in the same document at the same time, and you can watch other people's cursors as they type their ideas.
When you're brainstorming, create the environment your brain needs to get creative. Give yourself plenty of writing space and utensils; get everything out of your head and onto paper to make room for new insights. When you can, get yourself out of your normal workspace--go outside, or to the conference room with the great view, or to the coffee shop--to get the creative juices flowing. When you can, choose an open space with high ceilings. A 2007 study showed that people in rooms with high or vaulted ceilings tended to think more freely and abstractly.
If generating ideas is a regular part of your job, make sure you have tools you love to use on hand all the time. Splurge on a fancy pen or notebook, something that you love to write with, and take it with you on the train or to the dentist, and write whenever you have a chance, capturing any thought that might be useful.