If you want simple and effective LED lighting for viewing only, just look at the millions of screw-in Edison base LED bulbs.
Anything that tosses out around 150-200 lumens with a wide angle lens will probably light a 20g (high) easily... for viewing.
superbrightleds.com sells a lot of them.
If you want some good bang-for-the-buck LEDs, check out Satistronics.com
You can get a single, 10 watt LED, 10w driver, and surprisingly beefy heatsink for around $25. This will light up half a 55g easily for the eyes only... and maybe grow some low light plants.
Do not get their "warm white" LEDs though--- very yellow and ugly. Stick with "pure white" or "cool white".
They have 3w LEDs for $2 each.
None are going to be as efficient as a Cree or Luxeon, but that's not a big deal at all if you're not running a bunch and trying to save tons on wattage.