Nope, for pure-CS (not using CEL) projects, there's no alternative to CEGUI,
not counting old AWS and AWS2 which are not maintained anymore
(but one can find them in CSExtra repository
You could write your own with CS-only code, using csPixmap, for example.
CEL projects, like Crystal Core, generally use the "billboard" propclass.
And, there's the python-widget set in $CEL/data/library/blpython/widgets/
which Interstate Outlaws uses. There are now examples for it yet, apart studying
Interstate Outlaws or Ecksdee code.
And it's somehow broken with trunk/1.9 at the moment (but works with 1.4 & 1.2.1).