Sites On My IP has a number of nice tools on their site. The one I like the best is their home page Sites On My IP tool.
It’s a nice SEO Tool that can help you in a number of different ways.
1. Other way you can use this tool is to see how many other websites (and who they are) are hosted on the same server as your site is on. It is good to know how many sites your hosting company is putting on a server. If there are to many sites on one server that will effect your response time.
Also if you are looking at getting shared hosting you can ask the company for the IP address of the server they would be placing your site and check and see how many other sites are on that server.
2. If you are submitting your Website to a directory you can see if there are other directories on the same IP address. This can help you avoid a farm of directories.
3. Also if you are buying a site for some one that sells a lot of sites you can quickly see what other sites he has on the same hosting IP address.
Here are the other tools this site has that may be of interest to you.