ExtremeGB

 For one of the earlier Xbox emulators, ExtremeGB is a pretty damn good emulator. It says that compatibility is bad but most of the games that I tried worked just fine. Screen size is easy to adjust and can be adjusted even when the game is running by moving the thumbsticks around. Speed is basically 100% and I did not see any noticable slowdown. The GUI is really nice and includes a neat little 3d animation of a Gameboy bouncing up and down.

Features
-Easy to use controls
-Save/Load State support
-Customizeable game screen size
-Spiffy GUI

Problems
-Screen resize was a bit tricky to figure out at first.

Installation
Coming soon

Final Word
ExtremeGB is a really nice emulator, but, GNUboy has more options and a bit better compatibility.