When I went to college at Penn State, they gave me a "UserID" which is based on my initials. Because many people could have the same initials, they would follow it by a 3 digit number (I don't know if it is "Sequential" or not). Thus I ended up with PEG110. Many people think because they see "PEG" that I am a Female, but alas, I am guy (and happily married for 11+ years).
Anyway, it was "Unique" enough and memorable enough for me that it was just easy to use on the various sites that require you to sign up and RARELY have I tried to use it when I sign up does it not let me (because someone else has it). So if you see peg110 somewhere on the Internet, there is a pretty good chance, that it's me.