I've also enjoyed his "Merchant Princes" series. It's quite good. It's superficially fantasy, but not of the elves and dragons sort. It's really just the modern world, with one twist and everything the logical conclusion of that. The twist is that members of a certain family are able to "walk worlds" from an alternate Earth to ours. It then goes on to very logically follow how such a family would use this to gain power.

(Though I'm not sure I will forgive him for ending book three in a cliff-hanger...at least he seems to write fast.)

One oddity, though, is that he sets much of the action in the US (though the heroine is British), but the Americans use lots of Britishisms like "flat" and such. Funny, because those are often edited out for American release even in novels set in England.
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