http://toeflpractice.ets.org/ – The ETS official site; register and gain access to practice tests.
http://www.free-english.com/english/Home.aspx – this site requires students to log in, but once you do, there are tons of free resources related to English–including iBT practice and information on the test. There
are also monthly newsletters and other language learning programs.
http://www.testden.com/ – this site has a free iBT training online, but you have to register first. The other services are for a fee.
http://www.kaptest.com/repository/templates/ArticleInitDroplet.jhtml – Kaplan.com has a “mini” free TOEFL practice test if you sign into the site. There are also TOEFL “flashcards” available from your personal homepage once you sign into the site. The other services and classes are for a fee.
http://www.edufind.com/english/englishtests/index.cfm – this is not iBT-specific, but there are English language/grammar tests available that will help students preparing for the TOEFL. Many of them are free, some are not.