I use an app I wrote to do the sha1 so the sentence is not hanging around in bash history, but I do rely on the cmd prompt at times on computers at my house. Here's a screeshot of the app: http://i.imgur.com/tz255.png
No one but me uses it. So it's bare bones.
You mentioned adding a period for special characters but what do you do for passwords that require capitalization?
I suppose you could get that with base64 encoding rather than a hex digest. Something like:
echo -n 'Secret sentence Sitename' | openssl sha1 -binary | openssl base64Good idea. Lot's more space too when compared to hex encoding. I added it to my app: http://imgur.com/EcqZ1
Btw, do you ever worry that your command history might be accessed to discover your passwords?