I came across
MMOdata.net(site removed) the other day when reading the forums. It’s a site that estimates the amount of accounts each major MMO has. Some of the data is a bit outdated but it gives an idea on where a lot of the MMOs rank among each other.
It was cool to see that DDO had 110000 subscribers at it’s peak in 2010 when it went to it’s current free to play model.
Most MMOs are very secretive on their actual numbers so i don’t know how accurate the site is but it’s interesting information none the less.