Recommended: OU's Sefirat HaOmer reminder e-mails

The Orthodox Union will happily e-mail you a reminder every day of Sefirat HaOmer telling you what number you should count. Sign up here or here. Last year, with the help of the OU's reminder e-mails, I didn't miss a single day of the count!

In the meantime, here's a homemade reminder: Today [until sundown] is the third day of the Omer.