A perpetual calendar solves that problem by charting the months without naming the day of the week for each date. Find 5-by-14-inch calendars for $10 at galison.com. You can also download a printable perpetual birthday-reminder calendar (for free) at hallmark.com, or use the birthday reminder pdf.
Similar to a perpetual calendar but used exclusively for birthdays, a birthday book allows you to jot down birthdays without having to rewrite each date yearly. Keep it somewhere visible, though, such as on top of a coffee table or on your desk, as opposed to placing it on a bookshelf, where it may get lost amid your Steinbecks and Angelous.