As everyone said, Las Vegas is a shopping heaven, and there are shops absolutely everywhere. If you want to be a bit more systematic about it, however, the following would be helpful.
1. As Mo said, Forum shops at Casears have both high end stores like Bvlgari, Burberry, Christian Dior, Fendi, Versace and regular stores like H&M, Abercrombie & Fitch and an apple store. This place is also interesting architecture-wise and there is a show at the Atlantis fountain at every hour, I think.
2. Miracle Mile shops at Planet Hollywood also caters to many different budgets:
http://www.miraclemileshopslv.com/shop.php
3. City Center is the new addition to the midstrip. It is definitely high end. A huge Prada store is the piece de resistence. It has designer stores that I didn't even know existed in brick and mortar form.
http://www.citycenter.com/
4. The other easily accessible mall from the strip by foot (especially if you're staying at North Strip, like Venetian, Treasure Island, Wynn or Encore) is Fashion Show Mall.
http://www.thefashionshow.com/
If you want to hit the outlet stores, you will need to take a cab:
http://www.premiumoutlets.com/......asp?id=61
I was there in March. The weather will be even warmer next week, the pool season will be open. Don't forget to bring your swimsuit.
If you forget any necessities (like suncreen, flip flops, etc.), there are a few huge CVS and Walgreens stores on the strip. Also good for buying snacks and water. One thing I didn't know before I went to Vegas is that the city water is potable but tastes absolutely disgusting, so you need to buy lots and lots of bottled water.
Souvenirs and alcoholic drinks are cheaper in Fremont Street.
