Just a note - I pulled out a string of old white christmas lights to see what they would look like. These weren't LED, just old-school incandescents (the small kind). What I found was you need a good number - like the whole string - to make an impact in a large tank! I am not using these permanently but it was a good test. I think the LED's will be brighter anyway.
I couldn't find any LED strings for sale yesterday (it being after Christmas and all), so I think my next step is to "borrow" a couple strings off the in-laws for a more permanent installation!
And as for the DIY nature... this one really couldn't be easier. I'm just going to staple-gun the string to the underside of the cabinet. I'm also going to splice-in a dimmer and attach the string to a timer, but that's not necessary (or difficult).
Interesting links tho... those multi-colour ones are very cool.