just finished a small conversion of SDLCtrls (http://sdlcontrols.sourceforge.net/) to work with Lazarus/FPC. All the four tools and the demo now compile in Lazarus. However, I made an own package SDLLazCtrls (sdllazctrls.freepascal-meets-sdl.net) but in general it should be able to provide an updated package of SDLCtrls which is working in both environments. Since I don't own Delphi I'm not able to check for compatibility though.
For those not sure what SDLCtrls is: It is a fully working GUI (Forms, Buttons, Checkboxes, Scrollbars,...) purely done in SDL by Igor Stojkovic. A form designer is provided as well, so you can create new forms and menus just as easy as in Delphi or Lazarus itself.
I'm aware that there are many GUIs for OpenGL, however this one seems to be the only GUI which is SDL only.
I think about using this in a project. Feel free to try it out as well .