ABSOLUTELY hands-down the best cases are made by NUTSHELL.
http://www.tuff-as-nuts.com/
They cost around $40-50 each, but the belt clips NEVER break. They have a 2-year warranty, and they can be custom configured to have additional things, like retention straps, pouches, velcro enclosures, etc.
I had one for my Treo700wx and it fits the Mogul/Titan perfectly. I love it. WELL worth the extra cash to have a case where the clip doesn't break in 2 months.