Hi, Nicole:
I'm not sure which books are the best exactly. But I can tell you that in China, books published by Beijing Language and Culture University are the authoritative in this field. That university itself is the best in teaching foreigners Chinese. Also, it is said that Foreign Language Teaching and Research Press is very good. Because it is the authoritative press house in publishing foreign language books for Chinese. So you can imagine it also makes good books for foreign Chinese learners.
It's just like that the website of BBC offers learning English programms. You can also get some good Chinese learning materials on China's national TV station, which is called CCTV. There're some videos there. As a national TV station, they have the perfect Mandarin pronunciation.
Hope it helps.