go to nikonusa.com
and see what they offer
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Take some photos of yourself in the nude with the camera I'm sure he will be happy.
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Get him a 50mm 1.8 lens if he doesn't already have one. 50mm lenses are essential for any serious photographer and they are also the cheapest lenses you can get costing at around 170 to 200 usd. The next cheapest thing you can get for the camera is either an extra battery pack (which is also quite important) or a tripod.

Or you could get him some polarizing filters for the lenses he already owns, just check which lenses he has and ask at the store which size polarizer fits those lenses.
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What's your budget?

SB-600 external flash: ~$230
50mm f1.8 lens: ~$120
MB-D80 vertical battery grip: ~$140, add battery (the vertical grip takes two batteries so the camera can shoot more pictures before your boyfriend have to recharge his batteries) +$40
Bogen/Manfrotto tripod: depends on the model, but you can get a good one for about $200

All of the above are a great addition for your bf's camera, but if you have something else in mind, don't be afraid to shoot me an email.
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Get him a good book on photography, there may be one dedicated to the D80.
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A sturdy tripod or monopod. Bogen/Manfrotto is a very good brand.
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Does he have a nice tripod?
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