AnalogX IP See is a free online IP calculator and decoder that allows you to quickly and easily see the information about netmasks, address ranges, broadcast addresses, and more. The primary difference between this version and most others is how information can be entered; the simpliest method is to just type in an IP address. The next is to enter an IP range, such as 184.108.40.206-220.127.116.11 and it will return as much information as available about the block. Finally, you can enter a range in the abbreviated CIDR method such as 18.104.22.168/24, this is especially handy when fiddling with BGP tables or similar types of data.
If you find IP addressing interesting for some reason, I would recommend going to Subnet Online
which has a wide variety of information, along with the best description of how IP information is calculated.