This little known museum has an amazing collection of soviet era helicopters and even some jets. It is run by a private collector who has built up the collection over the past ten years. Rarely seem outside Russia these copters and planes are impressive and interesting and if you have an hour whilst waiting for your flight can be seen for small fee
www.aviamuseum.org/EN/
Ten min walk from the main terminal...ask the helpful staff on the information kiosk inside the building as other staff seem unaware of its existence (as do official tourist info in riga)
full info and list of exhibits here
aviamuseum.org/EN/
Only bettered by the equally unknown air museum at east midlands aiport (ask in aircraft model shop...the only one I have ever found in an airport even though that would seem a great place for one!)