You can take a look at TOEFL practice online, which is ETS mock exam.
However, the speaking and writing sections are computer rated which might not be really accurate and it's also really pricey.
(If you decide to buy it, there is a discounted offer for two of this when you sign up for the test)
I would suggest you to buy the ETS books for practice questions.
The official guide also comes with the test software which is not too far of from the actual test. (The speaking and writing sections are not rated though.)