My favorite, by far, is the new cold cathode 18W PAR bulb from Ushio. The model is 3000538. It is not cheap, but it works which is saying a lot when it comes to dimmable CFLs.

Make sure that you are using a Lutron or Leviton dimmer made after 1995. This goes for all dimmable CFLs.

We have used the GE21716 which is a dimmable R40 CFL. It just didn't cut it. Neither GE or Feit are at the cutting edge when it comes to dimmable CFLs.

Granite_Man

Here is a link that might be useful: Ushio 3000538

I used a Philips dimmable R30 floodlamp that buzzed *loudly*, especially when dimmed (with a high-end Lutron dimmer from after 1995). I had to move it to a non-dimmed location to get it run quietly. This dimmer switch controlled about 8 recessed lights, the others still had halogen light bulbs in them, not sure if mixing halogen/incandescent and CFLs on the same dimmer is problematic.

Cold cathode is excellent if it's available and you can afford it.

It is unwise to buy the cheapest lamp available and expect it to work well in a fixture for which it is not designed. Go to a professional electrical supply house and ask for their advice and be willing to pay more for better good brand like Sylvania. The cost efficiency of a lamp depends more on how long it will last than its initial purchase price.

On Feb 9 2009 I purchased 5 two packs of the FEIT Electric ECObulbs Dimmable Compact Fluorescent 23W=100. In the first week 3 fried. I spoke with their customer support and explained what I have and on their suggestion I replaced my 1000W digital dimmer switch with a 600W mechanical dimmer switch. I went back to Home Depot and they cheerfully replaced the bulbs. Since then 5 more have failed. For those of you that haven't done the math thats 80% failure in eleven days. today is Feb 21 2009. Unless FEIT can come up with a reasonable explanation for their products dismal performance I will be returning all 10 and going back to incandescent.

I am an electrician and did research. I called Leviton (a dimmer company) for a workable dimmer/bulb combination. They have not had good success or lamp life from their dimmers and any brand of bulb.

I then called Lutron (another dimmer company) for the same. They have had good success with only two of their dimmers and only one brand/type of bulb.
Their guidance>>>>>
http://www.lutron.com/CMS400/page.aspx?id=22117

Can find these dimmers and bulbs with an Internet search. I would suggest only the above referenced models together for longevity. (Dimmable CFL bulbs cost 3 times regular CFL.)

I purchased 12 Neptun dimmable 16w R40 bulbs 16 months ago. 4 have already burned out. At least they provide a 2 year warranty but shipping costs for 1 bulb at a time gets expensive. Has anyone else experienced such a high rate of failure from dimmable bulbs?