For a great 17.3 laptop case I recommend the Sharpcase laptop computer bag. They come in two sizes, one for 17.3 and 15.6, so make sure you get the right size. Most laptop cases out there are 17 Inch laptop bags. I went though several before I found one that would fit my 17.3 Inch Dell.
These come in 9 colors including black, blue and pink just to name a few. The best feature of this bag is that it is light weight. The case if fully zippered, and the large inner space holds the laptop. it came with a divider to separate the laptop from the space where the cords can be stored. There are straps with Velcro to hold the 17.3 laptop in place. Also, theres a front pouch for holding all kinds of accessories like phones and mp3 players and another zipper compartment for files on the back.
This case also has a strap on the back for attaching it to the handles of rolling luggage carriers. This came in very handy this summer when traveling. This case has been very durable, holding together despite the fact that I use it very often. This is quite surprising for a case that is less than $50.
The handle on top is very comfortable, but the bag also came with a color matching shoulder strap which is removable. This will give you some options when you decide to pick up that huge laptop and go. I high recommend this bag for your laptop. It was affordable, it has been durable, and you have several choices of colors to pick from.
Here is a link to a list of Top 10 Best 17.3 Laptop Cases, a great place to get more ideas.
Here is a link to a store that sells this 17.3 Laptop case.