Need a new iphone case, iphone 4s?

I'm in need of buying a new iphone cover. I have a white 4s.

There are many, many places that sell phone cases.
The varieties are VAST, from simple bumper style to enclosed bullet-proof versions.
If there's a shopping mall near you, go visit and take a look at what styles appeal to you.
Keep in mind, the production costs to make these are like 25 cents, yet they sell for $20 bucks. That's why phone stores love selling them - most Verizon stores will make more in accessory sales than phones and contracts.

You can check the used market as well, Craigslist has "never been opened" cases that you can get for $5 bucks, but you're limited to whatever they have.

Consider what you need. If you're prone to drops or hard knocks, consider the more robust cases like the Otter Box. If you're good at caring for the phone and want something stylish, then you have many more options.

Good luck and congrats on the iPhone 4S.
It's the best phone for the buck out there.