This is the first hard case I've seen for the Mogul and it's a winner:

http://www.wirelessground.com/spmoxvmoalca.html

I got it off ebay for just under $22.

Pros:

The tinge is tight (almost too tight).

The clear screen protector is great for quick access without having to open the case.

All the edges are well protected.

Con:

Not really Monaco's fault but with all the buttons and access points, a lot of the Mogul's sides are still unprotected.

No place to put an extra MicroSD.

Overall a good buy.

I prefer the seidio one.  I didn't get the rubberized slim case, but got the clear instead:

http://www.sprintmogul.net/Forum/tabid/54/ptid/370/threadid/875/forumtype/posts/Default.aspx

Scoob said :

This is the first hard case I've seen for the Mogul and it's a winner:

http://www.wirelessground.com/spmoxvmoalca.html

Have you noticed any decrease in signal strength with the metal case? It's been often cited that a metal case can interfere with the signal, but I'd like to hear it first hand from someone who actually has a metal case.

I've read about radio problems with metal cases but so far I've done ok without noticeable problems.

Of course, the few times that the calls sound weak or BT skips may be due to problems with the Mogul itself or the metal casing. Hard to tell.

I bought the NazTech Gladiator II case for mine.. Fits like a glove, and feels nice and solid.. Also has loops for a pen and a mini-flashlight..

Case can be found here

I got the Seidio rubberized case, and it's really great.  It fits nice and snug, and gives the phone a really good texture to ensure that it doesn't get dropped.  The only problem with it is that if you have a cradle for your Mogul, it won't fit in the cradle unless you take the case off.  Regardless, it's still worth it.