http://yuyin.baidu.com/

支持iOS和Android平台，支持离线，不用审核

http://mac.hk/appletalk/viewtopic.php?p=270931 - 嚴重痙攣患者对Ekho的需求
http://pitl.homedns.org/tts/demo00.asp - 港韵 TTS
http://sepc495.se.cuhk.edu.hk/cuvocal/Default.aspx - 中文大學「悠揚」語音合成系統
http://tdc.putonghuaonline.com/tools1.html - 看漢科技有限公司的 "e-Putonghua 網上學習平台"

a secret of the third tone
Falling-rising.
Third + Third = Second + Third: nǐ hǎo should sound like níhǎo.
Third + Second = Half a Third Tone + Second.

句末时第3声会有变化：

The 3rd tone can be produced in three different ways:

first half of a "3rd tone",

second half of a "3rd tone",

full 3rd tone