Well the seo account I have never monetized in any way. I just started building it because I thought it would potentially be a valuable account.
I basically followed people that follow a variety of high profile SEO companies and webmaster companies.
I also tweeted RSS feeds from SEOMOZ, Search Engine Land etc.
And as I said, no spam, no adverts etc. I consider this to be quite a good account with definitely genuine followers (for the most part).
The 2500 one way follower account once again I haven't used, it started as a backup for my main 24k account - it has a pretty woman as its front, its a mixture of ppl that tweet teamfollowback, followers of other pretty chicks etc, I also have loads of pictures of the chick in the profile which at some point I planned to post
The big account is a mixture of teamfollowback, producers, musicians, rappers etc - This account I was using for a while to sell "twitter management services" which I have a couple of people paying a monthly rate for twitter management - this was actually getting some interest so I know my followers are real people (or a percentge of them are).
But, I am getting out of that idea now - I have had too many accounts banned, so Im thinking about building twitter accounts then selling them - then If some get banned while Im building them it don't matter and I'm not under pressure.
Aside from that, I have started building a few blogs and I want to buy articles for them, but my paypal balance is sitting at zero - hence why Im considering trying to make some cash.