One place to find free aptitude tests online is at Aptitude-test.com. The site offers a wide variety of aptitude tests and test preparation tools, including articles and interview strategies.
The site contains a large selection of aptitude tests grouped under a number of different categories: numerical aptitude, verbal aptitude, non-verbal aptitude (such as abstract and spatial reasoning), mechanical aptitude, mixed aptitude and various other tests. The site also offers informative articles and aptitude test preparation strategies for specific tests, including the Armed Services Vocational Aptitude Battery, known as ASVAB, and the Canadian Forces Aptitude Test, known as CFAT. Aptitude-Test also features interview preparation tips and common interview questions as well as a smartphone application for test preparation on the go.