I take back what I said, for two SF and fantasy series. I'm still waiting for David Gerrold to finish
A Method for Madness, the fifth book in the War Against the Chtorr series. The fourth book was published in 1994, and included a teaser for the fifth book. I believe Gerrold says that the entire series will be seven books (if he ever finishes it). So all you Game of Thrones fans have nothing to complain about, and anyway, Neil Gaiman says "George R. R. Martin is not your bitch".
SALE ALERT:
Tor.com has about 50 ebooks on sale for $1.99 and $2.99. I'm not sure whether there's a link for this at Amazon, Kobo, et. al., but here's one at
B&N. Most of them are novellas, but at least one is a novel that Tor gave away last year.