I've had great results with the PIAA Ion Crystals... been running them since 2000, and I use them every day as DRL's. There was a brief stint where I tried Yella Hellostars, but they burned out within a month and they weren't nearly as yellow as the PIAAs.

Both bulbs seem a little dimmer than stock though, which I expected from tinting a bulb yellow.

 

Where can you get those lights?