The only basketball trading cards I own is the small series of cards that were included in the mid-nineties in Kellogg's serials for a few months. That was the time B-Ball really got more popular here in Germany and I guess they tried to get this stuff established here. But it never worked out...
I'm not saying that no one ever bought a pack of cards (I didn't, because I was more into collectible card games. With NBA cards you can't even play - how boring *g*) or that there weren't some hardcore collectors here, but it never got any widespread attention, not even among B-Ball fans.
But we do have our own tradition here in Germany for collecting useless, sports-related packs of collectible items: Soccer-Stickers! This has been a tradition for generations of youngsters - the tradition has it roots in 1890 - to spend their allowance on every new edition of stickers that is released every new season. There is always an accompanying sticker book where you can put your stickers sorted after teams, situations and whatever the designers have thought of this year. Although I do believe that the stuff does not sell as good today as it has in my youth, it is still widespread and you can leave a huge impression to any guy your age by stating you had the soccer albums of '86 - '92 fully complete.
But there is always the possibility to cheat, making this less of an accomplishment. When buying the closed and randomly assembled sticker packs there are always some few stickers that seem to evade you, no matter how many packs you buy, although there is supposedly no distinction between common, uncommon and rare stickers (mostly around 300-400 per series). And if you could not trade for the missing pieces with your buddies, you could always just order them at the publisher for a few cents per sticker. That of course makes it necessary to claim that you have completed the album without ordering any stickers at the publisher if you want to impress anyone.
I would also like to add, that there are always other sticker collections based on the same system (300-400 stickers in closed packs, cheaply sold sticker album) themed with popular cartoon series, recent movies, animals or whatever might catch the kids' interest. But the soccer albums always had the most success, which might come at no surprise if you consider how incredible popular soccer is in Germany.