I've played 3/4 of the games mentioned here. RuneScape I play very often, if anyone else would like to add me - Mayonaka_Cc is my RSN.
Americas Army is a lot like BF1942, it's a very good game. Infact, I'm going to redownload it now. If you like Counter-Strike, Medal of Honour or either of the Battlefield games then Americas Army is a good choice. Apparently it was originally designed to be a simulator training program for the American military forces.

Battlefield 1942 - Also good. Personally I don't like World War II games though, I prefer present-day. Battlefield 2, now THAT's a good game. If only my computer could run it, hehe.