Oaks Pavers offers a lot of information on their site.  You can look at specific wall types such as ultra walls or cambrian designs.  Within these specific wall sections, they also offer information on standard units, cornered units, step constructions as well as curve constructions.

If you need any help with obtaining materials or ideas for your retaining walls, Versa-Lok's site is for you.  The site has many useful sections such as: FAQ's, product descriptions, installation tips and a glossary.  So no matter what your knowledge level is, the site should be helpful to you.  They also offer landscaping ideas to assist with your creativity if needed. 

For a more detailed listing of Halquist Stone products offered through Old Fort Supply, visit their site.  On this site you will find a very thorough product gallery as well as some other useful information.