General Electric JEM25 800 Watts Microwave Oven

This is a solidly made microwave, and it is explicitly made to hang under a counter or inside one. It is much less deep than most countertop models - under 13inches. So if you have a lot of clearance between your countertop and cabinets (the "standard" is 18 inches, but I have 24 inches in my kitchen), then it means the microwave doesn't take up counter space. But if you have the standard 18" it won't help much to mount it under a cabinet since the door will run into things when it opens.

You pay a bit for the under-the-counter feature - the microwave is about 50 bucks more expensive than others, and you have to spend another $15 for the mounting brackets.

By the way, the new models of JEM25 have a turntable (that you can switch off for an oblong pan), and come in black, white, and stainless at extra cost.