Well I'm in a decent mood today, so I think I'll make a small, representative list of the groups (well at least for some of them) I already mentioned and maybe even add a few new ones.
GermanFarin Urlaub: (lyrics included)
Sonne - Sad song. Video has nothing to do with what it's about. Farin enjoys making silly videos.
Dusche - More rocking song. Very well known and very unusual content.
Am Strand - Happy song. Beware the black humour.
Die Ärzte: (lyrics partially included)
Junge - Lovely song with a mix of slow and rocking passages. The lyrics have a couple of typos in them, but the quality of the sound is good.
Nichts in der Welt - Sad song.
Pro Zombie - Happy song about zombies. No lyrics though
The music vdeos of those two are often sort of silly (in a good way) and have nothing to do with what the song is actually about.
Loving it.
Sportfreunde Stiller: (no lyrics included)
Ein Kompliment - Had this stuck in my head for a long time.
Silbermond: (no lyrics included)
Durch die Nacht - Don't know to much about them. They had their breakthrough with this song.
PolishGolec Orkiestra: (no lyrics included)
Sciernisko - One of the polish bands, I actually liked.
Lornetka - Another fine song of them. Slower than the previous one.
They have a "goralski"-accent, but the lyrics are slang free (might be a bit tricky for you though).
Let me know if those links are even available to you.
I'll be adding stuff, if anything should come to mind.
Couldn't find
anything much good from a polish band though.