I have a credit union account (First Tech CU), and I regularly deposit checks at a different CU's ATM (BECU has fancy ATMs that scan checks, so I prefer them).

In fact, any CO-OP Network ATM works just as well as my own CU's ATM (no fees, deposits, etc). They have locations nationwide, as most credit unions are members.

Edit: also included in that list: most ATMs at 7-Eleven.