Look into a free or cheap dynamic DNS service. DynDNS, freeDNS, no-ip, are just a few of the ones available and compatible with most ISP’s.
That would probably be the best way to go without having to go through the trouble of setting up and maintaining a webserver of your own.
A quick Google Search will give you quite a few more options including open-source versions of the services.
You could also set a cronjob or python script to send your external IP to an email account. Where at the very least you could retrieve the info if you find it has changed since you last used it.