A improvement of BrickedKeyboard watercooled redpower 2 reactor:
http://imageshack.us/photo/my-images/847/20111020122625.png/
http://imageshack.us/photo/my-images/511/20111020122630.png/
http://imageshack.us/photo/my-images/830/20111020122638.png/
Output:295 eu/tick
Efficiency: 3.93
When properly cooled with water buckets its a mk1 else you better run for your live. My relative compact water cooling system can be seen in the screenshots. Based on Brickedkeyboard reactor but improved alot :). Requires no maintenance except refueling once setup.
IC2 components:
1 nuclear reactor
4 reactor chambers
Glassfiber/HV cable to transport the eu (not shown in screenshots but can be easily added).
Redpower 2 components:
1 deployer
3 transposers
3 filters
1 timer
And some red alloy wires and pneumatic pipes
Vanilla components:
A ton of buckets for the cooling system
Bedrock (which i used for testing purposes here but normally use obsidian)
2 Chests
Thats pretty much all you need