I actually prefer to write in an online journal, I had a lot of issues with family members finding and reading my written journals. Invasion of privacy not withstanding, it always caused problems because of the topics I wrote about.
Penzu.com is a free one that automatically saves your writing (I had a different one but lost my writing too easily when the computer did something or I hit a bad key)

I find it very useful to get the thoughts out of my head, and often if I go back and read over some of it, I can see patterns of behavior (mania, depression, etc)