You can purchase glass tops and a light seperately, depending on what you are going to do with the tank will depend on what type lighting you will want to go with.
You can also go topless, of course depending on what type of fish you are going to keep in it because some are jumpers and/or escape artists.
There is also the option of going to your local glass shop and getting some glass cut for it, or plexi glass. Plexi glass does tend to bow inwards over time though.
I'm sure some others will chime it with some suggestions as well