Well I couldn't name you a list of applications besides telling you to look at www.freshmeat.net
But to run kde or gnome applications you don't need to install the complete kde/gnome environment. Just need gtk or kdelibs for the applications to run. It might be a good idea to install at least one of the two which will give you a whole range of applications which you can use which are based on these libraries.
You are probably running the version of Opera which is compiled with static libraries. So you'll have a overly large version of Opera. If you install some of the libraries then you can get the version of opera which uses shared libraries to save space.
I know you are worried about limiting space so you don't want to install a bunch of libraries. But I think you will be saving space by installing at least one set of libraries. All the graphic applications can then make use of the same libraries instead of having them statically linked in each executable.