It depends on how serious the DDOS and if you expect it to continue. Switching to another host and not letting them know about your situation could result in some unpleasantness.

There are hosting providers which specialize in hosting sites which are under DDOS attacks.

Depending on your needs (shared, dedicated, etc.) you might want to investigate a number of different companies. In the past I've found webhostingtalk to be an OK community for knowledge about this sort of thing.

If you just want a name for right now, I've heard ok things about http://www.blacklotus.net/ . They do shared hosting, dedicated servers, or if you want to keep a server farm on something like EC2 they do reverse proxying (although since you use 1&1 I'm assuming that your probably on either shared or a single dedicated box). There may be better providers out there, its been a long time (thankfully) since I've head to look into this sort of thing.