Nmap is very powerful and is a great tool to use.
Recently however I was introduced to a very simple to use app called Fing.
Fing is an app which is available for most smartphones and tablets. I run it off both Android and an iPad.
Simply install it, and then load it up. It analyses your network and returns a list of all the IP Addresses and the Computers name associated with them. It really is that simple!
Here is the entry for my Raspberry Pi, which clearly shows the IP address is 192.168.1.110.
Fing is such a simple and easy tool to use I am sure you will find it indispensable in no time!