As for DVDs:
http://www.cdjapan.co.jp/list_from_code ... &media=DVD
might be your best bet. I think I ordered something from them last year and it arrived no problem.
I haven't seen all of these, but my guess would be that the order of greatness is:
1. Wonderland 2003
2. Wonderland '95
3. 1998 Sing Or Die
4. Wonderland 1999 Fuyu (Winter)
5. Wonderland 1999 Natsu (Summer)
6. DCT Clips V1
7. Wonderland '91
Note that if you are in the US all of the above except #6 are Region 2 DVDs, requiring region-free hacks etc. to be viewable on US DVD players.
Wonderland 2003 is pretty good since it has all of their latest stuff, and doesn't have the 3rd guy who left the band in 2001 (?) any more, which is a net positive really.
Wonderland '95 is the favorite of all the ones I have since it is DCT at their peak, and the set and staging is fresh, and Miwa really put on an amazing show.
The 1998 Sing or Die concert is a more intimate venue and the last 40 minutes is really really good, almost like being there. Plus the concert's opening is pretty cool too.
1999 Fuyu/Natsu are both good. I have 1999 Fuyu, but I like 1995's WL better. Less obnoxious dancers, better numbers, much better sound.
DCT Clips is a collection of 8 or so videos, most from their MGO album. This is probably better than getting MGO maybe.
I'd like to see WL '91 to just see what DCT was like in the early days.