Beolingus is a good onlne German-Englsh dictionary.
The call number range for printed German dictionaries and other language books begins at PF3001. There are many non-circulating dictionaries in the Reference Collection on the 2nd floor of Alden Library. For volumes which you can check out, try the same call number area on the 7th floor.
The twelve-volume Duden series of word books is worthy of note:
We have many additional dictionaries. Here are links to listings in ALICE:
We have a many books on German grammar and usage, mostly in the PF3111 call number range. Here are a couple of sample titles:
Here's a link to search results in ALICE for many additional books on German grammar, mostly in the PC 2100+ call number area on the 7th floor.