Kay, I used to watch Digimon series since around Form 1 or slightly earlier than that. The series which I had watched is zero 1 to zero 3. Each of them are awesome in their own and unique ways, and nonetheless, the theme songs of theirs are all superb.

So far, I prefer Digimon 3, Tamer, the most. It has quite a nice plot (though not as good as 1 and 2), but the OST and songs from the series are all awesome. I'm obsessed with them since I first hear them until nowadays.

Let me intro the songs from the series :

Themes
1) The Biggest Dreamer - OP Theme (Cantonese version by Raymond Lam's the best)
2) My Tommorow - ED Theme 1
3) Days - ED Theme 2 (Best and 1 of the most touching Japanese songs I had ever heard)
4) 3 Primary Colour (A soothening song)
5) Slash! (This song really owns, due to it has a really nice music of rock type)
6) Evolution (Quite a nice evolution theme, but still prefer 1st and 2nd series one)
7) Kaze (Don't know where this theme came from, but still it's quite nice)

Character's Personal Themes
1) Across the Tears - Takato's Theme
2) Moonfighter - Ruki/Rika's Theme
3) Last Piece - Ruki/Rika & Renamon's Theme (Another touching song from the series. The tune's so nice)
4) Mirai - Jenrya's Theme
5) Anytime MouManTai - Terriermon's Theme (Quite a cute song from Terriermon)
6) Digital Survivor - Akiyama Ryo's Theme (Rock song, nice one)
7) Seta Ikkei - Cyberdramon's Theme
8) Fighting Soul - Akiyama Ryo & Cyberdramon's Theme
9) Culu! Culu! Culumon - Culumon's Theme (Another kawaii song! Damn cute one)

These are the nice one. Still got some others which are nice.

Other than that, there are still some theme songs from previous series like Butterfly (OP Theme), I Wish (Ed Theme), Brave Heart (Evolution Theme) from Series 1; Target (OP Theme), Itsumo Itsudemo (ED Theme) from Series 2.

Really recommend hearing them, since they're awesome japanese songs. Don't discriminate them because they're some sort of 'childish' anime in your eyes; you never know how good it is when you had spend your time in watching and absorbing the essence from the series.

Don't judge a book by it's cover; and don't ever let people's words affect your point of view on something...

I hope I can find some people who shares the same interest as I am. If ya want the songs or any songs from the series, try asking me. I'll be gladly sending you any of them if you want ^.~