An opengl render, in this sense is no different then a normal render, they both open the same window. What kind of new window rendering opens is set in the render settings as the Display.
It sounds like you have the Display set to Image Editor (the default).
In that mode the UV/Image Editor will take over the 3D view. You can simply press Esc and you will be brought back to the previous editor. Or you can change the editor, left most button in the editor's header.
Now if the display is set to Full Screen the UV/Image Editor will take over all of blender. Here again you can simply press Esc to get back, or you can press the "Back to Previous" button that will appear in the info header. Do not change the editor type. If you do change it, say to the 3D view then go "Back to Previous" the info window that should be at the to of blender will be changed into to UV/Image Editor. Odd I know.
I have always have the Display set to New Window, that way it opens a new floating window just for the UV/Image Editor, and nothing in blender changes.