I recently discovered this page, Invasive Species in Britain by frankbeswick.
I'm a big fan of this topic and I like how this page covers both animals and plants (I've touched on invasive plants in some of my pages but have yet to talk much about animal species). I also see that this page has already won an Editor's Choice award, so I'm evidently not the only one who likes it, but I just want to say I really appreciated it and it's one of my favorite pages yet.
I also found it really fun to read about invasive species in a different eco-region. There are some interesting overlaps as well as differences between the U.S. and the UK. For example, Japanese knotweed is invasive both places, but I was surprised to learn that Rhododendrons (which are native here) are invasive over there.