Been about a book per series so far so still plenty to go and he hasn't finished yet, I think another two novels are planned. So far there's five books but a couple of them are so big that they're split in to two.
7 books in total for the song of ice and fire series. The only worry is that the series may not get finished. The 6th book is being written now but I'm sure I read somewhere that his health is failing. Hopefully those rumours aren't true.
I haven't heard anything about his health but I have heard rumours that the writers for the TV series are the only people who know who A Song of Ice and Fire/Game of Thrones will end, so they can continue the series if something does happen to him.
I was reading the books after each tv series which worked fine for the 1st 2 series. The third book covers seasons 3 & 4 and so after reading that I decided I might as well the rest of them and there are some serious twists coming up.