Some nice carry cases can be found on Ebay or Here

If you know some good place to find some good cases, share here.

I purchased this one:
(about 60€ in its "vintage" execution)
Not received yet, will let you know my evaluation.

Does it have a belt hook???

No belt hook: that is why I choosed it ;-)
Other models from Noreve do have one.

Last minute: I have to travel abroad tonight for 4 weeks, so I will review the case only next month, as I didn't receive it yet.

I am back home and the case was waiting for me.
Overall evaluation:

1. Excellent manufacturing quality.

2. The colour shown in the web site is very different from the real one: my case was made of raspberry red suede instead of natural brown leather. However, I corrected this with plenty of dark brown shoe polish... Now I can say it's a "vintage natural leather" case...

3. Due to the incredible number of input/output devices built in the E90, and due to the laudable concern the manufacturer has shown about keeping them accessible, the case finally has many "holes". This reduces protection offered by this beautiful leather case: the external screen and keyboard, the ON/OFF button, the PTT button, the camera (with its button), the flash LED, the loudspeakers, the microphone, the connectors, the memory card bay are apparent. This leaves little room for effective phone protection.

4. The device can be opened to use internal screen and keyboard while enclosed in the case. However the opening angle is limited (just few degrees above right angle)

Globally, it's a success. Those who want to protect their E90 in an aggressive environment may want to buy something else, more like a closed box like this:
http://www.noreve.com/images/Nokia_E90B_case_Black.jpg

For heavy duty protection, you may alo consider this: (in aluminium)
See here

I had a similar case for my old 9500. Very satisfied with it.

This one (Proporta) can be a good choice too:

However, "leather" actually means here "plastic" (high quality though). Belt hook supplied.