Here is a recent announcement from Kiplinger summarizing IRS recent rules changes related to donations:

Even small cash donations aren’t exempt from strict record keeping rules, according to IRS’ final regulations. For charitable monetary gifts of any size, you cannot claim a deduction unless you have a canceled check, a bank record, a credit card statement, or a written receipt or e-mail from the charity with its name, date and amount of the gift. Pay stubs or W-2s work for payroll deduction donations. A blank pledge card from the donee for the donor to fill out doesn’t meet the rules. A contemporaneous written acknowledgement from the donee is also required for all gifts of $250 or more, describing the donation and whether the donor got anything in return.

You can view the regulations in full here.