Thank you all for your feedback. I love that this thread is taking off and I'll try to respond to as many points as I can.
Regarding the main discussion of 128 gigs being too small, I think there are plenty of cases where it certainly is just that, too small. However, I am a college student, so I probably don't have to tell you all that I'm a media junkie. I realize this makes the case for more internal storage, but bear with me here. For things like music (I have 40 or 50 GB), movies (~400 GB but adding more all the time), and photos (30-40 GB) I wouldn't mind using an external 3.0 or thunderbolt drive because these things aren't accessed daily. Sure maybe the music category, but that's from my iPhone most likely. Therefore, I wouldn't mind grabbing the little 2.5" 2 or 3 TB drive for those days I need it for whatever reason. I don't have a big boy job yet, so I'm not doing any business traveling. Would be more along the lines of a small trip or vacation and a run-of-the-mill hard drive would be fine in these cases.
Speaking of music, iTunes Match is holding on to my songs in the cloud for me, iCloud and OneDrive have my photos, but my videos are indeed vulnerable. As one user mentioned however, I would get a backup drive for my external drive to minimize risk and just to have for physical copies in the event of a massive Apple or Microsoft data breach, mutant overlords, nuclear war, etc.
Someone mentioned the "made for Mac" branding on some drives. I've always known this to be a scam on the technologically challenged, so not only is it good to avoid to save money, but also because those universal drives are blank slates and can hop between OSes right out of the box, correct?
If you really are a media junky, I'd rethink 128GB. I use external drives a lot, as I mentioned above, but there are drawbacks with that. Among other things, you should seriously consider having an actual duplicate, as opposed to a backup, if there's anything you care about and can't easily copy from somewhere else. External drives are easily dropped or lost.
Another thing to think about is that you need to keep a decent portion of the disk free to ensure good performance...you don't want to have, say, 121GB used on a 128GB drive.