How to Create Secure Passwords

As a web developer or any kind of internet professional, you naturally end up with loads and loads of logins. Maybe you use LastPasss, KeePassX or MyPasswordSafe or some other service/program, as long as you don't store them in a password protected word/spreadsheet file, or your browser! You don't do you?
Anyway I recently had to create a new password for a particular online service, one that I want a good secure password for, but starting to use a new secure password can be tricky.
How can I make a password long and include several special characters, upper and lowercase letters and numbers, and still make it memorable?
I had a brain wave that resulted in a really easy to remember password that is 21 characters, has plenty of special charecters, numbers and letters.....