Functional beats decorative any day of the week. The best gifts I received are a money clip, which got me to drop my giant overstuffed wallet. You'd be surprised how little you actually need to carry.
The other was a personalized set of casino quality poker chips, personalized with my face on them. Each man got his own face, so it wouldn't be weird.
Other good gifts included the flask (everybody needs one, but since it's a large group of friends, the first guy to get married used that), maglights, cufflinks, golf stuff, Leatherman tools, swiss army knives, buck knives, one guy did engraved axes. Looking back, weapons and tools were quite popular
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. All engraved, of course. I have also seen bar setups, and glassware (not the best idea if you ask me, I'm not drinking out of a Joe and Mary together forever stein).
Like anything else, the Internet has most of the standard ideas. If your crew has a common interest, then something functional to that end is probably the way to go.