I've have plenty of great Roleplaying memories. In fact, I have so many that it's hard to count. If I absolutely had to narrow it down, though, it would be this:

I've had a Roleplay that has been launched about three times now. The premise of the Roleplay is simple - the player is an original character that is sent to a world that rests in the middle of time and space and is basically entered in this tournament. This tournament is known as the "Ultimate Master Tournament" or "UM Tourney" which is the name of the series. Each UM had six characters of the player's choosing from different canonical worlds (and a likely useless mascot) and had to survive the tournament by taking one of the three brackets - one of neutrality, one of connecting with your entire team and one where you crush all competition.

Anyway, this series ended up having seven follow-ups and each were about two years long. I only had one Roleplay partner and we only got to the third part, but my favorite memories come from this series. It was so silly and light-hearted, yet it could be dark and mysterious at times. It also helps that my Roleplay partner is still my favorite Roleplay partner to this day.