Green, it really doesn't need to be very complicated at all. If I were to build a LED lighting system for your 10 gal planted tank I would:
1. Buy 6 of these LEDs (Cree XR-E Q2 bin) http://www.dealextreme.com/details.dx/sku.2395
and run them between 700mA-1000mA. You should get 165 lumens out of each of these @ 700mA for a total of 990 lumens or 210 lumens from each @1000mA (total of 1260 lumens)
($3.53ea x 6=$21.18)
2.Go to ebay and buy a 12v power supply capable of at least 3 amps to give you room to add more LEDs in the future if required
3.Plan on hooking up 2 parallel circuits of 3 series wired LEDs in each circuit.
According to the datasheet ( http://www.cree.com/products/pdf/XLamp7090XR-E.pdf
) @ 700mA the LEDs forward voltage should be about 3.5v and @1000mA about 3.7v
Use this LED resistor calculator ( http://led.linear1.org/led.wiz
.) I would get a few different valued resistors because the LED's actual forward voltage will be different then the datasheet says and will probably be higher. Get 1 ohm, 1.5 ohm, 1.8ohm, and maybe 2.2 ohm resistors and use a multimeter to determine which gives you the correct current (aim for between 700-1000 mA.)
4. Go to ebay and get 5 or 10 watt resistors of the aforementioned values (very cheap)
5. Now all you need is an aluminum heatsink to mount the LEDs and resistors to.
-Good inexpensive heatsinks
Ebay has a lot of Aluminum plate stock that can be used.
7. Get a small 12v fan to circulate air across the back of the heatsink.
6. Hook it all up-You should now have a top of the line LED aquarium light capable of good plant growth for $80-$90 with no bulbs to ever change
*You may want to also buy some red, green, or blue LEDs to later add in to adjust the color renditioning of the LED fixture to your liking.
*You can always add more LEDs to the fixture in the future if your plants require more light
*Check out this thread where I roughly estimated that about 6,720 Lumens of white LED light w/40 degree optics = 250 watts of Metal Halide lighting.
If this is correct then the amount of light produced by 6 LEDs on your 10gal tank should equivalent to around 2.5-3 watts/gal
*If you don't mind spending more, you can get higher binned Cree's from the same website that puts out more lumens/watt although for the extra money they cost you will be getting about 20 extra lumens per LED so you can decide for your self if it's worth it.
*You can use a constant current power supply like this one http://www.ledsupply.com/lt-901018700p.php
to simplify things and cut out the 12v powersupply and resistor step. The disadvantage is that it may be more expensive and leave you less options for adding LEDs in the future unless you spend more and get one able of driving more LEDs.