Is a check made out to a church, as an unrestricted donation, but given in the memory of someone who has died, a valid tax deduction?

The money you give to the church is tax deductible. However, your donations can only be counted if you itemize your deductions on Sch A of 1040. Because religious organizations have come under increased scrutiny for violations of the federal ban on charity support of political candidates and causes.
Churches and religious organizations fall under the IRS's Charitable Contributions category, and donation deductions generally are subject to a limit of 50 percent of your adjusted gross income.
The easiest way to keep track of your offerings to the church is to put a check in the collection plate. Larger churches generally give end-of-the-year, donation statements that verify the amount of money you have given by means of offering envelopes. In fact, the IRS requires charitable organizations to provide a statement to donors who make one-time gifts in excess of $250.
To verify an organization's charitable status, you can: Check with the organization to which you made the donation. The organization should be able to provide you with verification of its charitable status.
Please visit the IRS website here for a list of most qualified organizations;Search for Charities, Online Version of Publication 78