I present you my application for the PSP, it's a Master System and Game Gear emulator. It's a port from the excellent SMSPlus with improved compatibilty and good speed. All my games now run without problem! Most SMS games run perfectly at 166 MHz and Game Gear at 133 MHz. Also, there is no more sound glitches ^^
It can also play GYM music files. Files are placed in a ZIP file, used as a playlist. 6 sample GYMs are included, simply load music.zip in the emulator directory.
Nice interface, skinnable and with a lot of options.
Save state images are generated in real time rather than being stored in the save file itself. Note that sonic blast gradients are rendered correctly.
You can redefine all keys, including shortcuts (like state change/save/load, turbo mode, pause, reset), and there is an auto-repeat feature. You can also set the in-game screen as a background, useful to continue at the heart of action.
Nice icons by Phoebius, backgrounds by Japi.
MMSPlus features a rich interface with simple effects and good useability. And it's fully skinnable.
You can download it here: http://oslib.palib.info/MMSPlus.rar
Note: I'm sorry, I must post it, I implemented GYM support during these last days and I had no time to extensively test it, so it might be buggy. Anyway, please let me know any problem you had with it