KMameleon is a slick and easy to use KDE XMame.
It supports a vast section of options provided by the emulator, and it supports X11, SDL and XGL versions of it.
KMameleon is not really "just another XMame wrapper". It has really simple interface for game selection with a really powerful backend, which it makes it user-friendly for anyone. For newbies there can be just a couple of clickable options, which are stated "fullscreen" for the mode and "rompath" in "paths" module.
As in the very same time you have whole lots of options for the advanced user and (new in KMameleon 1.0) a module to write your own switches in, so if there are some new switches, or you feel better to keep all "under control", you can use that.
Actually... I haven't seen any other _good_ XMame wrappers for KDE. There are 2, that I can name at this very moment: KMameRun (last release for KDE 1.1) and QtMAME, which is not that bad, but 1) natively is written in Spanish and 2) paths are fixed, and it doesn't honour the $HOME directory, and it's written purely in Qt.
That's not bad, but as KMameleon is natively written for KDE, it uses some of the KDE's nifty gadgets, like DCOP for having unique application and lots more.