I think you are unusually bothered by this - it doesn't sound unusual to me.
my boss came to me, asking me to give exact details as to my current
project and what technologies I am using, as he want's to place an add
for my replacement as soon as possible. (this done in front of the
whole team..so much for keeping things quiet..if everyone didn't know
they know now)
Your team would have to find out at some point that you are leaving, your boss could possibly have handled 'the announcement' better but it doesn't sound out of the ordinary.
I can hear them discussing my role, as well as the new candidates. Is this ethical?
Why do you think it's not ethical? You work there. You're presumably competent at your job. You are leaving (which you are perfectly within your rights to do). They need to replace you. This involves (but is not limited to) finding someone who can do your job, asking you to tie up any loose ends, informing other people of your work so the transition can go as smoothly as possible.
I kind of feel worthless. The only time my resignation has been
discussed with me is when I broke it to my boss.
It's not that you're worthless, it's that they need to prepare for you not being around, and find a replacement for you. It's bound to be a bit awkward because your duties and responsibilities will gradually be taken away from you, but that's just part of it. As Jon Story pointed out in the comments, they aren't talking about replacing you personally. They are talking about filling your role and discussing business requirements, not discussing you as a person behind your back.
People talking behind your back is never fun, but you need to understand that they are just preparing for work without you, which is perfectly fine. Also bear in mind - you don't have to listen to them for much longer!
If someone seems to be talking about you an awful lot, why not talk to them? "Hi [name], I've heard you bring my name up a lot. I appreciate it's difficult with me leaving the company and leaving things for others to sort out, but I'm happy to chat to you if you have any concerns about making the transition to my replacement." Then you might get them to talk to you about your resignation and make it "normal".
TL;DR: This is a normal part of the process, which is bound to feel awkward, but you'll be fine. :-)