I made my own, because my case stands just shy of 29 in. IIRC. I had made my window out of 1/8" glass, but unfortunately could not find any trim that fits for 1/8".
So I made them (glass company) make one the same size out of 1/4" safety glass with a 35% tint. Which went well with the "hammered Steel" paint from Rustoleum. And I was able to find trim for 1/4" too for another 10 bucks. Since my case was huge and solid steel (old server type case), the weight of the glass had little impact. I have had my case for 3 years, taken it to dozens of LANs, its my 'portable' lanning rig, and no cracks or chips in the glass yet (knock on wood). I did weld a handle on my case because my case weighs a 60lbs (the 162mm fans from frozencpu.com don't make it light). Solid Steel, huge real glass window, huge steel fans, a few more hard drives and burners than average comp, and you have my heavy a** case which I will never part with.
My advice to you, is to get glass, not plexiglass (if you can afford the weight, that is).