GE makes two of the largest models (1.0 cu. ft.) that will still fit in a standard 12" deep upper cabinet. The GE Spacemaker and the GE Spacemaker II and the GE Profile PEM31. If you are planning to get a microwave shelf that sits below the cabinet (which then can be at any height above the counter you wish) they can accommodate considerably deeper microwaves, but they stick out. I'm not a fan, but it is much cheaper than custom cabinets.

There is no standard height, depth or width for microwaves. I used AJ Madison's website a lot to compare microwaves.

- Jim

Here is a link that might be useful: Microwaves at AJ Madison

Many people have a half-cabinet and then a shelf built below it (and attached to the cabinet above it). The shelf often extends past 12" even if the cabinet does not.

Additionally, more and more people are going with 15" deep upper cabinets rather than 12" for more storage and, sometimes, b/c many of today's plates no longer fit in 12" cabinets.

If you use 15" deep cabinets you could probably have an 18" deep shelf...but I would check w/a carpenter about it (you could try here). If you can use an 18" deep shelf for the MW, you greatly expand your choices.