A series available at Baen that is sort-of similar to Glen Cook's Garrett PI series is the
Thraxas series. Thraxas is a middle-aged, fat PI who drinks too much, gambles too much and is perpetually broke. He's also a pretty decent investigator. Fantasy setting, relatively hard-boiled style, corrupt local government, etc.
These books are somewhat more in the direction of humor or satire, but they are also pretty good mystery/detective stories.
Xenophon