Measurements may be just a little off but not by more than a few mm.
Techen - Looks like that could indeed work, I certainly like the idea.
Livewire - I am going to keep Java Moss (maybe Java Fern) but seeing how the tank should get some sunlight those lights could work.
daize- Don't think my shrimp would appreciate that too much
Lots of options really... You could basically just head over to the local hardware store and find something that sits on top. Are you planning to keep it without a lid, or are you going to put a lid on it in the future?