I have a bad habit, and that's of buying domain names. I have about 20, with several different registrars. If I was smart, I would consolidate them under one registrar, but, even then, checking expirations on the domains is a pain. I usually have autorenew turned on, but I still like to know when they are getting close to expiration.
Before re-inventing the wheel, I did a Google search, and found Domain Expiration Check Shell Script. It worked pretty well, except for a few top level domains like .me which didn't work. I modified the script, and just had to put some finishing touches on it today (.com, .net, and .org was broken). Check out the gist of the script on Github.
I put all of my domains in a text file, and can then run it with
./domain-check -f mydomains.txt. It's pretty cool.