Here is an example of an Asus laptop from Newegg that is a just bit more than your budget. It has one of the latest i5 processors - although not the top end of the i5 processors, it should be fine for Lightroom and work reasonably well for CS5 as well.
What I do is check out Newegg, Amazon and maybe something like CompUSA online to find a laptop in the approximate price range - then you can do some comparison shopping. Once you narrow things down, it's always a good idea to google reviews of the specific model you're looking for. Notebook Review is a good place to check reviews and user feedback. If you are more comfortable buying from a local store - like Best Buy, Costco, or a local computer store, you will be armed with info before you talk to a sales person.
If you have acccess to a discount buying program from work or school, it's also a good idea to check there - often companies that use Dell have employee discounts as well.