Korean music in general doesn't interest me. There's nothing wrong with it, really, it's just not my style. If you like it, though, there are plenty of dealers at the permanent flea markets with stacks of CDs, DVDs, VHS, and cassette tapes. Yes, VHS and cassette tapes are still available in South Korea. Now, the music video above is labeled as being North Korean, but the general concept of 1980s and 1990s style South Korean pop music is pretty similar.
T-ara's "Roly Poly" music video - this clocks in at over 12 minutes, but you can skip ahead to the music.
But modern K-Pop has... more pop. Synchronized dance moves, good catchy rhythms, and pretty women make for a nice show. I don't really have a favorite group, though since coming to Japan I've been introduced to plenty of K-Pop girl groups that have songs I like: Kara, T-ara, and Girls Generation come to mind.
Kara's "Go Go Summer" with a shorter opening skit.
I've mentioned before that Korean consumers aren't that into merchandising, except for some very important exceptions. But K-Pop is popular in Japan, too, and many groups go on tour here. And to go with the tastes and wallets of Japanese fans, there are some souvenirs produced for many of the groups.
SNSD/Girls Generation's "Gee"
It's my coworker who really introduced me to Girls Generation, singing the above song several times. And it's probably my new favorite. Pop music from Korea is just so peppy that you have to be happy. Or you should stop trying so hard not to be happy. I've only seen stores selling K-Pop goods in tourist locations, such as Itaewon and the tourist goods sections of shopping malls. There are keychains, buttons, posters, calendars, notepads, cloth photo banners, name tags, magnets, and a whole ton of other stuff. I found some business card-sized cards (they probably were printed on business cards) in a store in Japan, each with a different photo, with a set featuring dozens of photos of one band. Those would be the most interesting to me, but Korea didn't have those. I found a pack of postcards for just a couple bucks, though, and Girls Generation seemed to be the group to get.
Since these don't carry manufacturer's details, copyrights, or anything else like that, I'm not sure how "collectible" they are, but I like finding pop culture goods like these.