Her Majesty's Revenue and Customs (HMRC) website - this is the place to go for your tax admin and (if you're feeling brave) all the info you need. If you're not feeling brave, then stick around here and we'll try to make it simple for you. We try to give you a link to the relevant HMRC page when we do an article anyway.
We all know and love it - if you haven't heard of it, then get over there and check it out. It's a huge community of people just like us, asking questions and helping each other out. We like it so much that we are now partners of the site.