And the winner is . . .
Martin's Chinchilla Highrise, gutted of shelves & ramps, with Slide-Out Pan option

Photo from Martin's Cages (click on the Chinchilla Pictures link above to see Tango's cage with wood shelving replacing the metal shelving and ramps)
Why? In an ideal world, I would want to order a metal cage fully loaded with wood shelving, a hidey house, metal wheel, hay rack, water bottle, hammock, and food dish, but to this day I have not been able to find a single retailer that makes it that easy! (Hey, if medicine doesn't work out for me, I may give the cage making business a shot!) Until then, I have found Martin's Chinchilla Highrise to be the best out there and I have been extremely happy with its quality. This heavy duty, metal cage is the ideal size to maximize a chinchilla's natural desire to jump and stretch his springy little legs. It measures 30"x18"x48" with ½" x1" bar spacing (small enough that a baby chinchilla would not fit through). This cage features two doors, one high and one low. It is strong enough to support the weight of the Flying Saucer or Chin Spin wheels (or the equivalent, if you find one) and is built to last the chinchilla's lifetime. It comes partially assembled with easy instructions for completion and custom "pliers" that have divets to more easily grasp the metal rings that you use to hold the panels together. I also used small needlenose pliers to tighten all of the metal rings to avoid rattling when Tango runs on his wheel.
My one negative critique of the cage is that it usually comes with wire shelving and ramps. A chinchilla, of course, does not need ramps to get from shelf to shelf and they can be a potential hazard if toes get caught in the holes, about which I have heard one sad incident. I can't imagine it would be very comfortable to walk on all the time anyway! My recommendation is to call the company when you place your order and request the cage without the shelving or ramps. As of this summer (2008), I was issued a $15 discount for this modification. I replaced these shelves with kiln-dried pine shelves, which will be listed in a subsequent "Favorite Things" entry.
The slide-out litter tray design is great because Tango doesn't have to step directly on the dirty litter, I don't have to worry about him chewing on the wood shavings, and it makes cage cleaning a breeze! We have purchased 2 of these cages, one for home and one for "grandma's house", and they have served Tango well. This is especially a great option if you have a pair or trio of chins residing together. If you purchase this cage, I advise wiping it down before use with a soapy sponge and hose in order to remove the residue from the welding process.
Martin's Cages' Chinchilla Skyscraper is also an acceptable option from this retailer, though I do not advise purchasing a cage smaller than 30"x18"x36" if you can avoid it, especially if multiple chinchillas are residing in the same cage.
Where can I buy it? http://www.martinscages.com/products/cages/chinchilla/
How much does it cost? $150 plus shipping for the cage and slide-out pan upgrade. Call Martin's Cages to request the cage without shelves and ramps for a $15 discount.
While seemingly expensive, this cage is GREAT value when you consider how sturdy and long-lasting it is - I would be very surprised if you ever had to replace it. I figure the life span of the average chinchilla is about 15 years, so split up over his or her lifetime, it's only $10 a year - a good investment I'd say! The alternative would be to buy a lower quality cage for around $50 that you have to replace every couple of years and isn't made to support the heavy duty wheels like the Flying Saucer or Chin Spin.
Is there a close 2nd place finisher? Quality Cage's Chinchilla Mansion (http://www.qualitycage.com/) is another suitable alternative, with the added note that if you purchase the "Starter Package", do NOT use the dangerous plastic food bowl.