You could of course install some Mac OS X apps that can do this, probably at some small fee or ads. Well, here is a much better and non-intrusive method for that, thanks to lavoiesl of github.
First, download osx-cpu-temp from github:
$ git clone https://github.com/lavoiesl/osx-cpu-temp.git
Compile, and install.
$ cd osx-cpu-temp
$ sudo make install
To run, simply run