All birthday cards, all the time! My general MO to send birthday cards on time is to sit down with my perpetual birthday calendar about a week or so before the next month starts, and write out each of the birthday cards in advance. I then stamp and address them, and put a sticky note on each one with the date I'm to mail it (usually between 7-3 days before the person's birthday, depending on where they live). They are in chronological order in my things-to-mail pile, so when the date on the post-it comes around, I just peel off the note and drop it in the blue box on my corner.
These February birthdays are all pretty similar, with a bicycle theme. The border stamp of different cycles on the bottom of some of the envelopes was handcarved for me by Bethany of
TeaOlive, who does amazing work. I carved the larger step-through bicycle on numbers 17 & 19 myself, and the rest are commercially available stamps. I promise the blue ink shows up a lot more in person; the scanner light just washes it right out.
14/365, sent to Joe in Virginia Beach.

15/365, to send to Beth in Tampa.

16/365, to send to Steve in New York.

17/365, to send to my grandfather in Florida.

18/365, to send to Jessica in North Carolina.

19/365, to send to Billy in Chicago.

20/365, to send to Mindy in Maryland.