Pretty much any clamp fixture with a ceramic socket will do but if you want a brand name, then Fluker, Zilla, Exo Terra and Zoo Med make them. Zoo Med also has stands, but if I can recall they need to be tucked between the tank and stand which might not be a great idea with a huge tank. They (don't remember who) also have stands that use adhesive and you can stick it onto the glass. Others have used shelving on their wall and hanging plant brackets on the ceiling.
The main issue is to keep the lamp pointed straight down but you do have a number of options.
