This is a really tough tragedy to get involved from the outside, as bad as we all want do. There's no recovery effort, no clean-up, there's no financial donation that really hits an immediate need (other than making sure everyone gets counseling who needs it, and/or help fund a possible memorial or new school that gets built if they decide to tear down the old one), there are no major medical bills to help families with (at least I don't think so - two adults were shot in the leg, but no reports that they have long recoveries ahead). Really, the families most-severely effected just have to grieve privately.
I donated to the UConn fund, and to an Eastern Connecticut scholarship created in Vicki Soto's memory to help future teachers, but it feels like so little. Just browsing school websites, Western Connecticut also has created a scholarship for music in memory of Ana Marquez-Green (daughter of a jazz musician - Jimmy Green). St. Joseph's (Hartford) has created a scholarship fund in memory of Rachel D'Avino (niece of a women's Boneyarder) to help students studying applied behavior analysis and autism. Some of the families have funds in their child's name to help the families - the Emilie Parker Fund was created to help all the families, and the Noah's Ark of Hope was named for Noah Pozner.
Those are all financial, though. In terms of donating time, it's hard to know what to do - the streets of Newtown will be pretty quiet on Christmas. Everyone will be bunkered down with their families after the church services in the morning.