UPDATE as of 6/7/2014: I have created mobile versions of this game. The iOS version is the baby version of the same game. The Android version is closer to the original version.
When I thought about making my own Flappy Bird games, I immediately thought about my original SpermWorld game. You can find it on this page on my website. You'll need Flash to play this one.
As for the sequel, I've made it with Unity this time. Made this within a couple of days.