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Best random generic gifts: food, and drinks
Consumable gifts are always a safe choice, because they serve an actual purpose, and it's not a problem if a person receives twice the same thing (as long as they like it)
Just make sure the person is not allergic or on a special diet, or that their religion or whatever doesn't forbid them to eat/drink the thing, etc.
Also, pick up quality items, obviously.
Consumables also involve stuff like soap and perfume, which can be nice, but is a bit more risky: can be interpreted as "hm, plz use some soap, you stink"

... Also, it's difficult to pick up a proper perfume if the person isn't there to try it first (perfume smells differently on different people

also, tastes can differ greatly)
Another pretty safe, useful gift: accessories. Especially the "one size fits all" type. For instance, a scarf (perfect gift, especially in winter). My advice is to aim at functional (and nice-looking) rather than purely cosmetic (jewelry is soooo over-rated). But functional stuff that the person won't mind having several of: a large collection of scarfs is nice (mix and match FTW), a large collection purses (or watches[*]) is useless. A purse or a bag can make a nice gift, but make sure the person actually needs one... (also, some people have high usability standards and prefer to chose such personal, functional gifts themselves: make sure the bag is the right size, has the right amount of pockets, etc...)
[*] electronic gizmo such as MP3 players and cell phones and such are quite popular, but, being highly technical gifts, they're a very risky choice, IMO, if the person you offer it to is an expert and/or has high standards and/or specific needs
Lastly, I can think of entertainment material, such as books, films, music... If you know the tastes of the person well, they can make really nice, personal gift. But you must be very careful the person doesn't have it already. That's the biggest problem - reason why another popular gift these days is money/gift vouchers?

A pretty unpersonal choice, that one.
Oh, that reminds me, among consumable gift, there is also things like travels, concert/match tickets, etc. (think "service"). Nowadays you can get one of those "ticket for a good week-end" thing, and let the person chose exactly what they want (and when) in a catalog. Quite versatile, but still more personal than a generic gift voucher.
In general, try to buy stuff you're personally familiar with, quality-wise. Asking a seller for advice isn't always safe (some are actually helpful, but some just point at the most expensive stuff). Asking a friend/relative (or Google??) for advice, if you're not an expert in the field of the product you wanna buy, is probably a better idea.