If you've had great service, a helpful chat, or a positive interaction with any team member(s) of a company you do business with, I suggest you take down that person's name and title and send their company a "thank-you" note.
Someone did this for me once when I worked at a restaurant. I was away on vacation when it was sent in and by the time I got back and found out about it, it had been posted in the national newsletter for our company. Not only was I thrilled to have been noticed for my service, I was elated to know that the people who had given so much to me, personally, during their visit to dinner had also gotten something from me. What an excellent feeling! I still remember their names and stories years later.
I have definitely given my fair share of "feedback" to companies that haven't met my expectations, but I'm sure you've had other great experiences deserving of compliments and praise like I had recently with JetBlue Airways staff at JFK International Airport.
Most large companies have a specific form you can fill out with comments and/or compliments, others you can write simply to their "contact" information and they will usher it to the correct department.
Do something nice for someone who gave you great service.
Do it before you forget about it.
Why not make someone's day today?!
Judging by the way I feel right now, it might improve your own, too!