Now We Are Six Hundred is a book of Doctor Who children's poetry, though there's plenty in it for adults. It's written by James Goss, who wrote Dead Air (which you might remember me gushing about as the best DW audio book ever [but not audio play; that's a different beastie altogether]) and "Death and the Queen", my favorite of the Tenth Doctor Adventures vol. 1. The book is illustrated by none other than RTD himself, and I must say, he is an incredible cartoon artist. Some people are just so talented.
The book is fashioned after Now We Are Six, a book of children's poetry by A. A. Milne, and many of the poems copy the style/meter of the poems in that book, while others copy other poems or are completely original. The pieces are all different: there are some about specific people, some about specific episodes, some about eras, some about concepts or themes... All kinds of things. They tend to be sweet or funny, but there are some serious and heartrending pieces as well.
The poems also cover the entire history of DW; for example, there's one specifically about the Second Doctor's adventures with Jamie and Zoe, and even Adric got a poem. The modern DW poems focus more on the first four seasons than on the latter six, even though, as far as I can tell from interviews on the web, RTD didn't have input on the content of the poems.
In general, it's a fun read. The overall feeling is whimsical, but there are some gems of real meat in there (hm, that metaphor really didn't work, but I'm leaving it in because it's horridly silly). To whet your appetite, here are photos of the first poem. Enjoy!