I'm trying to teach a buddy of mine about artifacts, smearing, etc, etc so that he understands why I want him to use the best encoders etc. I was wondering if anybody out there knew of a good site that has a bunch of these samples already online?

Someday I do plan to getting around to set up a site with all this stuff, just been way too busy...

Have a look here. Browsing "Uploads" forum might be a good idea too.

for quick success, encode this file with Xing or an FhG encoder at 128k

http://ff123.net/training/training.html

I don't think that training to hear artifacts serves in "real life". Think about possible consequencies!

See what I've wrote some hours ago. I totally disagree with you: possible consequence are not purely negative.

I think it can make a fair difference, DEPENDING on what the mp3s are later used
for.
I dj, and I use third cd deck that plays mp3 cds [as a backup deck and for
my remixes] , if I was to encode some mp3 say at 128k or 160k resulting in files
that have some barely noticable, or unnoticable artifacts when listened to on some
2 inch pc speakers. Thats great if I played them on the pc only. But when I then
go to dj with these files playing through a full range system with 1 - 2 kW of
power, and sometimes using effects that may 'enhance' these artifacts?
You can probably imagine those 'real life' possible consequences.
I can often pick when a dj is playing a low/medium quality mp3, and I would
rather not have other people with a keen ear to be able to notice that I am playing
an mp3. So I use high quality settings like extreme or insane.

So just to summarise, I think that training to hear artifacts does serve in "real
life" - Depending.

Effect

I'd recommend you my Camera fragment. it's a real killer for many coders.
Differnce is obvious.