Few things:
Quite a few 'Simple 2000' games and other Japanese titles have been released in Europe, in English under the '505 Gamestreet' brand.
http://www.505gamestreet.com/
http://fuji.drillspirits.net/505/ < list of published games along with Japanese titles.
KuruKuru Kururin for the GBA was released in Europe (it was a launch title if I remember correctly) and you can pick it up for as low as $10'ish new on ebay.co.uk.
Likewise Sonicgems Collection came out in Europe on the PS2. =)
GAME.co.uk are owned by EB (we used to have EB, but EB bought out GAME then ditched the EB name in favour of GAME, or something like that), so they are certainly a reliable place to buy from.
Try EBAY! Seriously I have gotten some amazing deals on secondhand Japanese games, just try more than one search e.g. japan, jap, jpn, japanese, import, chinese, ntsc-j etc...
And check out Ebay.co.uk for European imports; major retail stores usually won't carry any old/out of print, and may lack some of the obscure titles; ebay is ideal for this stuff (think of stuff like KuruKuru Kururin for example).
http://www.ntsc-uk.com/ are quite a good site for import reviews and discussions if if hasn't been mentioned already.
As for game recomendations well for the PS2 most music games are worth a look, the Japanese versions of DDR, Beatmania and Taiko have MUCH MUCH better songlists than the US versions, can be used with US controllers and have loads of games in the series. I also recommend Pop'n Music ^^ (google it). The MAJOR exception here is the Karaoke Revolution Series which sucks major ass in Japan (the songs are all midi's, there's no romanji (english) lyrics, backgrounds suck and you can't use the US Karaoke Revolution Mics).
On the subject of Karaoke games if you like them then you MUST check out a European only series called
SingStar for the PS2. There are 5 games in the series so far with the 6th installment 'SingStar: Anthems' being relased in a couple of days (Each game is based on a different genre of music).
The games are STACKS better than the Karaoke Revolution series, the game mechanics are a lot better (it's much much easier to read and sing along to the music). Each game features around 30 songs (original recordings) along with the actual music videos and as you'd expect stacks of game modes. There are lots of nice touches such as being able to hot swap discs for other SingStar games without turning off the machine.
It's developed by Sony's London Studio (I think. i.e. The same people behind the EyeToy games) so of course also has optional EyeToy support.
Unfortunately you have to use SingStar microphones with the games, which will probably cost quite a bit to ship abroad, but that is because they are heavy, QUALITY mics, they absolutely trounce the crappy Karaoke Revolution mics by a mile. I recommend ordering from GAME as postage abroad isn't based by weight but per order - only £5). The retail is around £35 ($65) a game with 2 mics or £20 ($37) without mics
Check out
www.singstargame.com for the games in the series along with trackslists and music previews.
I can't really think of any other PS2 recommendations, though I would personally love to check out
Iuksa Gami, 'cos it looks awesome.
Oh and regarding the DS, a small correction... Jump Superstars isn't all that 'import friendly' IMO as some wins have to be under certain conditions, which you won't be able to understand. Saying that there's lots of info on gamefaqs to help you out though.
And Osu! Tatake! Ouenden! I think should be relabeled to 'import friendly'. - The "stories" before each song are illustrated on the top screen and in most cases it's quite easy to make out what the plot is about. The only thing you won't understand are the songs themselves, but dam they're catchy. Ouenden! is by far one of the best games on the DS I really can't recommend it enough.
Come to think of it 'Kaitou Rousseau' for the DS is also great fun, basically you disguise yourself by copying a background object on a piece of paper (e.g. a window) to avoid the cops and such, it's halarious, but there is quite a lot of dialogue; not import friendly!
Oh and for the GBA I have to recommend 'F-Zero Climax', it's the best GBA F-Zero yet and even features a track editor, very import friendly.