This one is from my favorite banned member of all time.
Step aside people, we have to include the best RANT of all time.
Suck it down you drunken bitch!
And please use the actual thread title in the link so the rest of us don’t have to click every ambiguous link to see if we’ve already searched for that thread. Thanks.
I rather suspected that the factual fora would be underrepresented. With that in mind, I present the Fabulous Über-Roach (ok, so it’s actually called “Upper Size Limits for Insects?”), An expanding universe? Am I expanding?, and Galileo, a Hammer, and a Feather (be warned, that last one is ancient).
I came to nominate that one:
I nominate Is there any reason that semen would be bad for my fish? As you can imagine, it starts out with a pretty punchy OP, and rapidly escalates from there.
There once was a thread about the tiresome aspects of being a porn star. It went along the lines of “I ordered a pizza and …” Can’t find it, though.
Dammit! I had just remembered The Grapist and was going to post one of his threads. Ah well. Great minds, etc., etc.
Threads which sucked us in (in a different way than, say the TMI thread or its derivatives), such as:
What happens on May 33 but only on leap years?
and
Anyone known the perpetrator of a really horrific crime?, which had a huge ratio of page views to actual posts,
and
Things you’ve seen that actually made your jaw drop
On a different front, how about Happy Scrappy Hero Pup’s Things that will never stop being funny. Ever.
or the dueling schlock song lyrics of If Life is a rock and the radio rolls me…
I’ll be bold enough to nominate my own Strangest high school team mascots in which bivalves, insects, flowers and stuffed animals are among the symbols designed to inspire fear and awe.
And how could we not include the wonderful self-referential, essence-of-distilled-threadness known simply as Thread
Why are there holes in the lids of some cans of Kiwi shoe polish? - ChiefScott
Here’s the special request write up, which is not the original thread.
http://www.straightdope.com/mailbag/mkiwi.html
This link mentions the original thread that was very interesting, which apears to be removed. It’s a shame that the original discussion is gone, it was a clasic.
What say the administrators? Does the original discussion exist anymore?
My first nomination will have to be:
Gotcha ya!
4 years old and still one of the funniest things I’ve read on the dope.
Second and third will be:
Root beer floats
and
Coke au lait?
Two unique and funny threads made great not by me, but by Anastaseon. They weren’t very long threads so I doubt very many of you remember them. Check them out, seriously.
Then you’ll just love this!
Oops! Screwed up the code on the “Did you ever know anybody that created a horrific crime” link. This is the correct link .
My apologies. I’m such a :wally sometimes.
Sadly, Cisco, it appears the pictures are missing. And if they are missing from there, then they are missing forever, unless someone saved them. 
in the banned doper department, can anyone find the Satan thread where he asks the SDMB whether or not he should let his girlfriend bonk him with a strap on?
Also, Wildest Bill had a couple of good one’s. I’ve searched but can’t find the gotcha ya one about his dream funeral.
I’m looking for “The most embarrassing thing you’ve ever witnessed” thread.
Coldfire’s thread has been linked, but if it was Memorial Day that you’re looking for, it might be my thread:
I have to nominate for one of the all-time best threads :
The Truth or Dare game thread.
Most. Fun. Ever.
I’m going through this thread right now and reading the nominated threads that I hadn’t already ever seen or known about…(so far at this post, 25 threads are on the “list”)…and I just had to reply to this.
I’m looking for best threads over all. Not just great OPs. Like you said, some of them I’ve read in this thread had funny, great, memorable OPs…but then just kinda drop off.
Some, I’ve found, have great OPs and then inspire or create great replies or similar stories…and those are the ones I’m talking about. Those…or just threads that were so amazing and great in general and overall that people love.
No doubt, by the time I finish reading this thread and the threads linked to, I’ll have more topics added to this list…but yeah, not all of them will make it. Like I said, up to your post right here, only about 26 are on it so far…out of about 30 or 35 already nominated.
Not that I’m the end all decision maker on it. I’m just tending not to keep ones that are only a page long or the like (with other things wagered in, of course–I mean, a thread could be one of the greatest SDMB topics of all time but only be one page long, just in here so far, I haven’t really seen it yet…I think one was a birthday thread, and another was a pit thread that kinda slagged off near the end. :p).
Keep them coming, though. Still probably need lots.
Okay, reached the end…and like expected, the number has increased.
42 topics have thus far been added to the list. I didn’t read ALL of some of those that had mucho multiple pages, but enough to know that they were truly some of the greatest threads. 
Just off hand, I can still think of about 12 or so topics that I thought were the best ever on here (and that get mentioned a lot of times all over), yet nobody’s nominated them yet.
I’ll give it a bit more before I’ll put them in myself. : p