Hmm...what would I want for a long term relationship anniversary.
If he's stylish and has the occasion to dress up regularly, perhaps a really awesome tie...like some of those really expensive ties that you'd find at Nordstrom's. Thomas Pink's website has some awesome, awesome ties...but I'm a guy who if I had the money would buy all sorts of ties, probably more than any other clothing item.
If he likes NBA basketball or NHL hockey you could take him to a game if there's a team nearby, particularly if his favorite team is coming through town (or is the home team)
Concert Tickets?
I don't know, just some ideas.
If he's also greek, perhaps some nice items he can hold on to for years. Simply go to
http://www.greeklicensing.com and check his organization's listing.