I'm sure you know that everyone is a little different, so if the person is your son or daughter (or niece or nephew) go into their room and see what kind of collections they may have. I like to collect manga, legend of Zelda manga, and lucky star, and other manga that I like from anime I've previously seen. If you can find what copy they have, like tsubasa book 1, you may consider looking for book 2 & 3. If it's a popular manga, it will typically come as a large book (3 in 1) with about a $ 20-25 price.
Purchasing blu Ray anime can be a bit more challenging and expensive, but you can always look on Amazon.com, and you can buy a used one for a decent price. If they like character figurines, you can buy one online, or in an anime store, which are sometimes in shopping malls.
Like me, they may be influenced by anime, and may enjoy the types of things that are shown in anime, like a personal computer or a Playstation Vita system. Most anime fans love animation art, so buying utensils specifically for that art style (copic markers) will probably make them happy also!
And I'm pretty sure any anime fan would love a poster, or even better- a wall scroll with their favorite anime, or anime character(s) on it. The same goes for someone who is a huge fan for call of duty, or bio shock, or portal,
and so forth. This is just a kingdom hearts photo - (a very popular game among us nerds) and final fantasy is a great option too, trust me. Just ask them! Chances are we're thinking about our favorite anime or game or whatever so much that we aren't catching on to your purchasing intentions :) we love taking about anime. Happy holidays^_^ I hope this helped you out. 
