have a look at liszt or thalberg operatic fantasias
Especially Thalberg as he rarely gets played.I am at the moment re-learning the Tausig-Weber-Invitation to the Dance. It is a splendid display piece with memorable themes. But like Thalberg, it is not played often.
Mendelssohn: Variation Serieuses (13 minutes)
Also you might like to try one of Schubert's Drei Klavierstucke these are good concert pieces, I am particularly fond of number 2 but all of them are excellent, it is performed around the 9-11 minute mark
If you (amanfang) can find the sheet music to Thalberg's Robert le Diable paraphrase, you'd be set. I don't know about the sheet music, though.
I have the sheets if anybody's interested...
I LOVE the mendelssohn f-sharp fantasy, but I played it last year. So I can't really use it again. Brahmsian, can you send me the Thalberg piece? I'll take a look at it. Although my guess is that it's probably too over my head.