I just finished a prototype which turned out so well I thought I'd share some details.
It uses 3x19 inch monitors magnified by Fresnel lenses to give a near-seamless 135° FOV. The lenses fool the eye into believing the image is approximately 7 feet wide and farther away than it actually is; more like what eyes are used to focusing on in real life.
It can be built for a little over $200 including the cost of cheap second hand 19" LCD monitors (plentiful in most areas). Here's a link to the lens I used: http://bhlens.com/product_detail.aspx?pid=34
The overall weight is only a few pounds (plus monitors); easily made lighter by detaching the monitor stands and hard-mounting, and the compactness delivers the small moment of inertia important for motion simulators.
Please note: I am in no way promoting the use of the wooden table structure for a motion platform

Now, I never normally get sick playing video games. However, the overall effect of this design is so immersive that I got quite motion sick and nauseous for the first few hours of trying iRacing with it. I think that means it's working

Technical Details:
The side lenses/monitors are angled 45° inward and each monitor is about 19cm behind its respective lens. This gives a roughly 1.7x magnification equivalent to a 31" monitor. My viewing position is roughly at the perpendicular intersection of all three lens centers. Overall resolution is 3840x1024. Each monitor is 1280x1024 and is a 5:4 ratio,19" diagonal in size. I would not recommend using anything over 20", nor any of the widescreen 16:9 monitor types as they are not suitable for the lenses which are 40x32cm. The 5:4 x3 ratio is perfect as you also get a nice vertical FOV too. Overall, the 19" size is perfect for this application. I recommend trying to find three with very similar image & color qualities, if possible.
I'm sure this concept is nothing new to motion rig builders, but I sure don't see many people doing it. Not sure why.... highly recommended!
One lap in iRacing:
http://youtu.be/kOMREPZNYwM
Walkthrough videos:
http://youtu.be/KjVFaZc9pw8
http://youtu.be/FpFnY_3QVcU
Pics: