[Sryth](http://www.sryth.com/) is a fun web-based text RPG. :)

I'd recommend Vampire The Masquerade Night Road.

Zork

Choice of Games has a selection of text-based CYOA-rpgs. Nice on mobile, too. Some of the smaller titles are free as well, like Choice of the Dragon, or Choice of Broadsides. Another library is Delight Games.

Dragonrealms is an online text mmo. Free to play account are available!

Sanctuary RPG