I purchased this
BookArmor case for my Kobo Touch, but also use it for my Kobo Glo. This one is actually for the Sony PRS505/700, but I wanted something roomy so I could keep a book light (which I no longer need) and microfiber cleaning cloth in it too. The case has about 1 cm of space around each side of the Glo. If I didn't keep a cleaning cloth in the case the Kobo might slide around a little bit, though.
The case is very sturdy, with a rigid plastic shell inside the cloth cover. I've been using it for over 2 years, throwing it in my messenger bag with all sorts of heavy things. It really protects! As a bonus, I don't have a bulky case on my Glo when it's time to read.
BookArmor makes a case
specifically for the Kobo Glo. It has added brackets to keep the Glo from sliding around. It's on sale right now too. (ETA: Whoops, TechniSol beat me to it!)
I wish Speck made a
FitFolio case for the Kobo Glo. I have one on my Touch and love it. But, even with the FitFolio, if it's in my messenger bag, it's secured in the BookArmor to ensure the screen is
really protected.