Aqueon - VersaTop
Aqueon VersaTops are glass lids that include: glass lid, plastic hinge, handle, and a plastic back strip. These lids fit on standard rimmed glass Aqueon tanks. If you have a different brand tank, these lids might not fit on your tank. Please refer to the above link for exact measurements of the lid.
Note: If you need a 55 gallon lid, order two of the 24in lids. Also, 2.5 gallon lids are a solid piece of glass with a handle. No hinge or plastic back strip is included.
Rivers to Reef says: Glass lids have many benefits: They keep the fish in the tank, they prevent evaporation, and they help to stabilize aquarium temperature.
The only time we would not really recommend a glass lid is on top of tanks where light penetration is essential (such as in high-tech planted tanks or reef tanks). Glass lids degrade light (from all light sources), and may prevent good coral/plant growth near the bottom of the tank.