Right now ICANN sort out all the gTLDs. It costs $10k to apply for a new domain, and it may not even get accepted.

A new company, I forget what they're called, are making a new system which should make it much cheaper & easier to introduce your own gTLD. For example, you could have .computers or .yourname, and it wouldnt cost nearly as much as ICANN's fees.

So who knows what the future will spit out, but .com, .net, .org, .info and ccTLDs will always be the leaders of the market.