The latest one I've enjoyed is The Carnival of the Feminists, which has a truly fascinating collection of articles despite its rather mundane title.
I've been hooked on The Tangled Bank, a bimonthly collection of articles on science & medicine (aptly named after Darwin's metaphor) for a few months now.
It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. From The Origin of Species, 1859; p. 450.
An interesting story about the (probably) real "Tangled Bank" and the tragic death of Darwin's ten year old daughter turned up in a story in The Guardian Unlimited when I searched for the page number for The Origin of Species quote. And a fascinating argument about whether Darwin actually said "tangled" or "entangled" turned up in the archives of the Society for Literature and Science.
Anyway, look at all the carnivals listed at Blog Carnival, sorted by title. There's everything from Asian History to Wine Blogging Wednesday out there - an entanglement of riches.