Okay, here are my five...

1) Audacity - great sound editing tool
2) Basecamp - project collaboration tool - I'd be lost without it!
3) Facebook - a great way to connect informally with clients & fellow VAs!
4. Business Balls - jam packed with useful info & links
5. DocStoc - Tons of useful templates

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"Instead of looking for things that have gone wrong and trying to fix them...Look for things that went right and try to build on them" Tom Peters