Buying gifts for anyone that has a lot of stuff can be hard, but items that can be used up or worn out are a good way to ensure that even if he has it already, he'll need it again in the future.
Wear and usable items:
(1) Tires, there is nothing like a nice set of road tires such as the Vittoria Open Corsa CX. Two more exotic brands are Gommitalia or Veloflex. Check your local bike shop, but you may need to turn to online retailers to find the latter two.
(2) Fancier energy food such as the Lärabars are a newer product that are all natural and unusually delicious for an energy bar; Costco sells them in bulk and most grocery stores have them as well.
(3) Personal care items such as chamois creams, warming oil, sun screens, and tech wash detergents are also items that are often overlooked when buying for yourself. I like Assos brand chamois cream and tech wash detergent. Elite Ozone is a hot new brand that has the media buzzing.
(4) Maintenance supplies. bikers go through a lot of bike chain lubrication and other cleaning supplies. Pedro's is a brand that specializes in environmentally friendly lubes and cleaners, which they often package in complete kits.
Last, depending on the person new technology items such as a Garmin GPS can also make a great gift, but may be ignored by a less technologically oriented cyclist. Other bigger ticket items may be King Titanium water bottle cages, Arundel carbon fiber water bottle cages, Assos shorts (e.g., F1 13 or F1 Mille), or Rapha clothing for a "classic look". Another options with clothes is to buy accessories such as socks, gloves, and warmers that are all stuff a cyclist will need eventually.