1. Online

GRC’s Ultra High Security Password Generator is a good choice when you’re out at a client site and need something random and secure. There is also a specific area for generating secure WPA passwords. You may recognized the domain as it’s the brainchild of Steve Gibson who is well known for his hard drive recovery product Spinrite and weekly co-hosted computer security podcast, “Security Now!”

2. On your computer

Use Keepass which also securely stores and manages your passwords. I highly recommend this tool. Watch my video screencast featuring Keepass’ Auto-Type feature which saves you from entering passwords in manually each time. Very nice piece of software.

3. In your browser

With this Firefox Extension, Password Hasher. I haven’t used this extension in a long time since I use the first two in tandem but Lifehacker reviewed it last year and gave it a thumbs up. It could be a great solution for you if you were running a portable version of Firefox and didn’t have access to the internet.
(Supports FF versions 1.5 – 3.0, updated September 1st, 2008).