First, let's start with a basic setup: I turn off Siri's audio confirmation messages - I don't need her repeating back things to me when I'm out in public. Next, I enable "Raise to speak". With this setup, here are my favorite commands (I bolded the words that Siri acts on:
Set timer for 30 minutes. Gives you a count down timer. Handy reminder to move clothes from the washer to the dryer.
Remind me to watch the news at 10 pm. Sets a timed base reminder. Unlike the timer, you can create multiple timed reminders (watch the news and move the wash over).
Remind me to take the hamburger out of the freezer when I get home. Set a reminder based on a location.
Where's my wife? Gives me a location on my wife.
Call my wife. Starts dialling - no need to look up the number.
Tell my wife "You look marvellous!". If she's setup with Apple's Messages, it will send the message that way. If not, it will send an SMS.
Tell my wife where I am. Sends her my location on a map (if she's using Messages).
Email Jimmy about dinner on Thursday. Creates an email message with "Dinner on Thursday" as the subject. Siri will then ask you what you want to say in the message.
Email Jimmy about dinner on Thursday and say "Where do you want to go?" Creates an email message with "Dinner on Thursday" as the subject and "Where do you want to go" as the message.
Setup a meeting for tomorrow at 10 am about "Meeting with Insurance Guy". Creates an appointment at the time indicated with the title "Meeting with Insurance Guy".
Setup a meeting for tomorrow at 10 am about "Meeting with Insurance Guy" with John Walker. As above, but invites John as a participant (you can invite multiple people too).
What movies are playing? Get a local list.
Show me how to get home. Directions
There are lots of other commands you can use with Siri - which ones do you use on a daily basis?
And don't forget that Siri loves to dictate notes for you!