All of Lyndsy Fonseca and David Henrie's scenes as Ted's (Josh Radnor) future children were filmed during the first season to keep them the same age throughout the series. This includes a scene for the show's final episode filmed early in the second season.
The husbands of three of the main actors have appeared on the show, each time as the significant other of one of the other leads. Alyson Hannigan's husband Alexis Denisof plays Robin's co-anchor Sandy Rivers; Cobie Smulders's husband Taran Killam plays Blauman, who might have a crush on Ted; and Neil Patrick Harris's husband David Burtka plays Lily's ex Scooter.
There are only 18 times throughout the entire series that Barney (Neil Patrick Harris) shows up without a suit. (However, these are often other suits, e.g., a snowsuit or a flight suit.)
After the show ended, Josh Radnor kept the blue French horn, Neil Patrick Harris got the Playbook and the gang's MacLaren's booth, and the three yellow umbrellas now belong to the director Pamela Fryman, as well as creators Craig Thomas and Carter Bays.