Per Jasmine's request and for her upcoming house-guests, a review of Portland. A top five was impossible. :)
A walk along NW 23rd will take you past a multitude of independent Portland shops and restaurants, ranging from Moonstruck Chocolate to Oh Baby (leave the boys outside) to Goorin Bros. Hats. For $8 you can enjoy dessert at famous Papa Haydn's. I recommend splitting desserts, and their french fries are delicious! For the less adventuresome, Urban Outfitters, Gap, and Levi's are available. If your friends are from a small town as I suspect, they will probably enjoy a ride on the max, a stroll through the heart of the city, and a look around Pioneer Place.
If your friends like vintage, check out this blog and take your pick.
For a different vibe, check out N. Mississippi Ave and take a peek through the delightful clutter at Flutter and you must partake of delicious to die for carnitas at Por Que No? You will also find The Meadow, a specialty salt store and a smattering of boutiques.
Whatever you do, don't let your friends set foot in a Starbucks! Albina Press, Barista, Stumptown, Pix Patisserie, and countless others serve a better brew and an authentic Portland feel. If they have learned to read, take them to Powell's Books, the largest independent bookstore in the world.
If your friends have not been to Portland before, take the time to drive out to Multnomah falls on either a beautiful afternoon or when the stars are peeking out.