Which tools would you use to capture business requirements?
Simplest tools are often the most effective.
We use basic excel and word to capture requirements.
Visio or tools like Smart-Draw are good for visualizing user interface quickly and showing them to the customer to get on the same page.
Recording MP3 files during meetings is an effective way to make sure you do not miss out of important points later. Also works really well if you have remote teams since it lets them “listen in” on the meeting if they aren’t really there and get a feel of the requirements first hand. Just record your requirement gather sessions and post them out on a server where everyone in the team has access to them. It helps.
Tools like Project Path and other tools from 37Signals are awesome. E.g. some features like White boards like you brainstorm, discussion feature lets you capture requirements through email and their task list helps you decide what does into which sprint. Not many bells and whistles but does the job if you believe in doing things the simple way.
I would suggest to read Business Analysis Body of Knowledge (BABOK), in order to get a complete answer.