Collectables?
Have a super cool hat you can put on to look gansta?
Music?
Have background music while you pop dem coppas faec off.
DRUGS?
just kidding lol.
Internet. People can buy websites where they have "blogs." People can buy computers (250$ or something) and use them to look at peoples "blogs"
it could be like an overlay, and the browser just shows what the player has posted.
Of course you would probably limit the customizability to what's displayed on the website, what the colors are and the way to access.
SIM Cards (Or something of the such)?
People need a way to securely transmit secret messages to each other, people could vend these little cards you could inscribe messages onto to give to others to look at/read
Books?
Have a few people in blockland write up some quick things like "Moby Block" and have a GUI display the pages. Could be something to use while waiting for someone.
Group Lots?
People can spend money on giving a corporation or a group of people a lot to build on, they all can build on. I know you can just give trust to people, but maybe they also want their own private lots, that removes that problem.
Holidays?
They can request (using big money) to have certain days labeled after them.
I don't know, I'm just thinking up of things I have stored in my mind as mod ideas.
Maybe they can request a certain icon before/after there name.
Poll