Note Tab Lite (1,796 K) click here Powerful Notepad replacement with spell-check, autocorrect, etc. (Direct D/L)
It remembers the file type you used last time, e.g. html. There are dedicated HTML editors out there, but Note Tab Lite is pretty similar to Wordpad, i.e. you should find it easy to adjust to.
For me, Wordpad defaults to *.doc so it must be possible to change the default, but not I think to all files. It will remember what you used last time for the current session only. Wordpad is just not the right tool for the job.