I prefer not to use dummy text, because creating wireframes and comps that reflect how they will really look and function is what people pay me for, and is a sign of a lazy IA/IXD. Plus it can be really enjoyable to write real fake copy. Having said that, I have to admit to being the lazy IA from time to timeand have gone to gone to lipsum.com to generate dummy text.
Another thing I do is go to silly blogs and copy the text there. Dwight Schrute's Schrute Space has been a great resource for that lately, since I'm working on a TV-related site with user generated content. This at least makes my copy look semi-real.
But if I have to resort to dummy text, I think I'll be going to the Blind Text Generator rather than lipsum.com. This dummy text offers you a few options, from Cicero's standby Lorem Ipsum greeking to a passage from Kafka's Metamorphosis. You'll never have to deliver boring copy again--in your wireframes at least.