Role-players can be hard to shop for, but I took a shot at coming up with five quality products that should fit almost any taste. Hopefully at least one of these should satisfy the gamer on you list.
For the GM in Your Life - Gamemastery: Combat Pad
The Combat Pad from Paizo Publishing will make life easier for the Game Master in your life, no matter what system he chooses to play. The combination of erasable surface and colorful magnets makes the chore of running combat easier and that much more fun. I own one and it is a really neat product.
For the 3E Fan Who Loves eBooks - Castle Whiterock and Gazetteer of the Known Realms
The Dungeon Crawl Classics line from Goodman Games combines old-school feel with Third Edition D&D rules compatiblity. Castle Whiterock is a huge mega-dungeon and the Gazetteer of the Known Realms is a complete campaign setting with adventures. You can get both in tree-friendly eBook format from DriveThruRPG for only $10 (original price $99!) until December 31st when they have to cease sales. That's literally hundreds of pages of game material for less than the price of a movie ticket.
For the Fourth Edition Fanatic -Dire Tombs
It's pretty darn hard hard to run combat in Fourth Edition D&D without miniatures and some sort of combat grid. Dungeon Tiles from Wizards of the Coast are an inexpensive and colorful solution. One fairly generic (and still available) set is DT6: Dire Tombs. It's got everything needed to build an interesting little dungeon environment.
For the New-School Gamer - Dungeons & Dragons Roleplaying Game Starter Set
If you want to pick up something for that really smart nephew, you could do much worse than the Dungeons & Dragons Starter Set. It has everything he'll need to get started, including rules, Dungeon Tiles, tokens (to use in place of miniatures) and dice. If you want to know more, check out my review of it HERE.
For the REALLY Old-School Gamer - Swords & Wizardry
If you know someone whose idea of D&D involves three little brown books in a box, pick up Swords & Wizardry. Matthew Finch's take on the original edition rules is well-written and (in my opinion) much more coherent than the rules it is based upon. The book looks nice too and you can get it from Lulu in softback for around ten bucks.