Today I was working in the recovery of an Atlassian Crowd 2.2.x installation and in the process I needed to get the base64 representation for an IP address (See https://confluence.atlassian.com/display/CROWDKB/Client+Host+is+Invalid) like this:

IP: 127.0.0.1
Base 64: fwAAAQ==

So I wrote a simple script and uploaded it to http://iptobinary.zz.mu/ so you can get it easily.