Partially a follow-up to this post of mine from a year ago, I note this article from c|net that discusses obsolete ports (mostly in computers). I think that everyone can agree that their choices of Parallel (printer) and PS/2 (older keyboard and mouse) are on the mark. Their choice of Firewire will be controversial because of its non-obsolete status on Apple computers, but after discussing it with my wife (who loves her iMac and iPod Touch), she agrees that on non-Apple computers it is; USB has replaced all three of those (and IMHO that’s a really nice thing :) In notebooks, PCMCIA was obsoleted by an increase in onboard components (e.g. network and wireless) and USB devices that do the same thing.
In terms of my personal experience, I should also point out that phone ports (modems) are quite obsolete; if you need one, you can always buy an external USB one; they’re quite small these days :)
On the inside of computers we have SCSI partially displaced by IDE, and fully replaced by SATA.
ISA replaced PCI, replaced in turn by PCI-e; AGP is also replaced by PCI-e.