There is the
Perfect Sunday offered by skimaxx. I have not been on any of those trips but they look like they might be worth trying it for a days skiing!
For weekend trips you might also want to try the
Frankfurt International Ski Club They are a mixed bunch of people and I had a great time when I went to Ischgl with them at the end of last season
Going from Darmstadt there is also the
ESOC ski club. I have not been any of their trips yet but my boyfriend raves about them and I'll be trying a few this season. They are slightly cheaper than the FISC trips. You do have to pay a bit more if you don't work for the space people but it is not very much and still cheaper than the FISC ones as they include ski pass.