There are many secrets or easter eggs that Nintendo has added to Wii Sports. Here are a few of them, if you know of another one add it to this page by editing
Wii Sports Review - IGN
Hidden Targets - Expert - Wii Sports Resort Guide - IGN
Showdown - Wii Sports Resort Guide - IGN
Cycling - Wii Sports Resort Guide - IGN
I Points 70-80 - Wii Sports Resort Guide - IGN
Hidden Targets - Intermediate - Wii Sports Resort Guide - IGN
Wii Sports Resort Nintendo Wii Video - E3 2008: (Off Screen) Demo Part 2 - IGN
Hidden Targets - Beginner - Wii Sports Resort Guide - IGN
I Points 50-59 - Wii Sports Resort Guide - IGN
Wii Sports HIDDEN SECRETS!!
3-Point Contest - Wii Sports Resort Guide - IGN