Alternative to Pogoplug? Wanting to access HD from anywhere

If I'm reading this correctly, you want to connect a hard drive to your network via a computer or NAS and be able to access the files outside of your local network over the internet.

This is more complex than it seems. Unless your ISP allows you to have a static external IP address (which most don't unless you pay extra), you won't be able to reliably find the drive online because its IP will change over time and often at random since the ISP is constantly juggling new connections.
A VPN (Virtual Private Network) can solve this, but setting one up can be challenging and the speed will probably not meet your needs if you're trying to play back media files. I'm not familiar with Pogoplug, but it seems like they're charging you to facilitate the operation of finding your volume over the internet.

Also, unless you have an internet connection with high upload bandwidth you won't be able to access your files very fast no matter how fast the connection you happen to be using is. In the US, most high speed internet is based on cable, which has abysmal upload bandwidth often peaking at around 100KB/s; not nearly enough to serve up media files over the internet.

TL;DR you're better off either bringing an external HDD with you or paying for some actual cloud storage via dropbox or some other such provider since they have fast, stable hardware with an extremely fast and reliable internet connection.

Caveat: I'm not a networking expert by any means, so if I've made a mistake here, please correct me.