I have been running these little LED light strips on my Ultimaker for a while. I had them lazily taped onto my frame, but finally whipped up a nice little mounting channel yesterday and thought I would share.

LED lights themselves:

http://www.amazon.com/gp/product/B0056Z036A/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Basically, you just take two of them stacked side by side and slide them into this channel, then bolt it onto the UM frame. I have one on the front and one on the right. This really helps with dialing a print in, as the bright, low-angle light helps show over/under-extrusion.

These LEDs are pretty cheap, and I have one dead bulb on 2/4 strands, but they have held there for quite a while now. Plus, you never really look straight at them, so it isn't obvious.

I had to do a little trimming on the LED strands to have them fit better. Near the wire end of the strands, the shape of the rubber flairs out a bit. You can just take a utility blade and carefully trim that area to keep roughly the same cross section as the rest of the strand. It won't be visible once they are in the channel.