I'm a big fan of Jim Butcher's wizard/private-eye-in-Chicago series, so I thought I'd give Simon R. Green's Nightside series a try. It seemed to have a similar premise: a man solves clients' cases with a hard-boiled approach and a soupcon of woo-woo powers. Something From the Nightside is the first in the series, and I think I'd have to read more to give Green a fair evaluation. The first one was a little shaky. Green had too many "best if you don't ask/know/think about it" references. My imagination is not all that great that I could fill in the blanks myself about what I didn't want to know/etc. The love interest, Joanna, didn't seem all that appealing, but John Taylor (love this hiding-in-plain-sight name, no Sebastian Ignatius Spellcaster moniker for him!) is sunk up to his thyroid before you can say "blimey."
There were some great fantasy ideas, including the concept of "Nightside," an alternate dimension hiding behind the London we know. John Taylor is a man-with-some-mysterious-powerful-potential who chose to flee his home in Nightside and live in our dull but safe world. He has a talent for finding things, and that's what he does for a living. There are about 11 books in the series currently available in the U.S.