I was recently turned on to some interesting websites for learning Esperanto and Toki Pona.
For Toki Pona, check out tokipona.info. (Chi tiu retpagharo estas en Esperanto.)
For Esperanto, check out kurso.com.br. This site has a Free Software (GPL’ed) program for learning Esperanto. It runs on Mac OS X, Windows, and GNU/Linux. I expect that it would run on other POSIX systems too, like FreeBSD and OpenBSD. Maybe.
Additionally, never forget lernu.net for a great (wonderfully multilingual) Esperanto resource.