There is an issue in the wording of uncanny dodge:
Starting at 4th level, a rogue […] retains her Dexterity bonus to AC (if any) even if she is caught flat-footed or struck by an invisible attacker. However, she still loses her Dexterity bonus to AC if immobilized.
It is unclear how broadly to take this. There is a case to be made for reading this as a very absolute statement.
If we read it as “a rogue […] retains her Dexterity bonus to AC (if any)” followed by reminder text, just for emphasis, that this applies “even” when subject to a couple of common reasons to lose Dexterity to AC, then a whole lot of things that would usually trigger sneak attack no longer do. From your list, in fact, only two things would work: sleep and helplessness (because “Rogues can sneak attack helpless targets,” even if they retain Dex to AC, I guess). The rest only work if the rogue is immobilized.
Note: D&D 3.5e did not define “immobilized” as a named condition in the core rules, though it is referenced several times in them, and so it’s not exactly clear when someone is or isn’t immobilized. For example, is someone who is climbing “immobilized”? They’re literally moving! But they’re also very limited in how they can move, which means they maybe can’t uncannily dodge. The rules are unclear.
Worse, later on, they did define “immobilized”–specifically as having your movement speed set to 0. This doesn’t seem to match the sense in which it was used prior to that definition. At any rate, not going to be using that, since there’s no way that Player’s Handbook (2004) was referencing a definition not found in the rules until Tome of Magic (2006).
Also worth noting, flanking clearly works even in the absolute interpretation. Flanking is almost-certainly the most common way of achieving sneak attack, so this is pretty important. On the other hand, see improved uncanny dodge, below.
However, this is not how this ability is usually played (as in, ever, in my experience)—it is generally understood as preventing you from losing Dexterity to AC only in the case of being flat-footed or struck by an invisible attacker. But—under this reading—there are other ways to make the target lose Dex to AC that aren’t catching them flat-footed or attacking them unseen.
The reason why this reading is so common—and so likely to be the intent—is because “she retains her Dexterity bonus to AC” as an absolute statement is weird in English. If it said “she always retains her Dexterity bonus to AC […], even if […]” then the presence of “always” would suggest an absolute statement, and the presence of the comma before “even” would separate that from the rest of the clause, making it seem more like reminder or emphasis. The way it is, the beginning “she retains her Dexterity bonus to AC” leads one to expect that the rest of the sentence will read “in these particular situations,” and so that’s how most people read it, despite the fact that the actual words used are “even if.”
But “even if” are the words that are there, which now makes things weird. It’s a counter-intuitive sentence either way, and suggests that the words were chosen poorly here. In a strict rules-as-written sense, the case for reading uncanny dodge as absolute is pretty strong. In context, it’s pretty weak.
Skip Williams trying to have his cake and eat it too.
And it turns out there is a third approach here. Skip Williams basically side-stepped this issue in his Rules of the Game: All About Sneak Attack (Part 3) article. He states that uncanny dodge protects against flat-footed and unseen attackers. The wording suggests this is a complete set of things it covers. He then uses an extremely broad understanding of “immobilized” to allow many, many situations to deny one’s Dex to AC even with uncanny dodge. This covers climbing, for example.
More importantly, he kind of implies that every single thing that causes the loss of Dex to AC falls into one of three categories: flat-footed, invisible attacker, or immobilization. If it’s not flat-footed and it’s not invisibility, suggests Skip, it’s immobilization and therefore not blocked by uncanny dodge. This works out the same as our second, non-absolute interpretation, but for different reasons. I haven’t gone through every single thing in the game that denies Dex to AC, but I have my doubts that all of them neatly fit into one of those three categories and there isn’t anything outside them, personally. On the other hand, Skip worked on the design team for the Player’s Handbook, so maybe his understanding reflects, at least, the understanding that the authors intended.
Maybe. Part of me kind of suspects that Skip noticed the “even if” issue, and came up with this “interpretation” as a way of maintaining the behavior they wanted without admitting they messed up the wording of it.
What still works against non-absolute uncanny dodge
Anyway, assuming uncanny dodge prevents a rogue from losing Dex to AC only when that would happen because of being flat-footed or attacked by someone you can’t see, that opens up a lot of ways to potentially sneak attack a rogue. From your list:
invisibility does not work—uncanny dodge says so.
blinking does not work—“You strike as an invisible creature,” see above
feint works—“You can also use Bluff to mislead an opponent in melee combat […] your target is denied its Dexterity bonus to AC (if any) for the next melee attack you make against it,” no reference to flat-footed or invisibility.
sleep works—“A helpless character is […] sleeping, […] Rogues can sneak attack helpless targets,” period, end of discussion.
stun works—“A stunned creature […] loses his Dexterity bonus to AC (if any),” nothing about flat-footed or invisibility.
cower works—“A cowering character […] loses her Dexterity bonus (if any),” nothing about flat-footed or invisibility.
climbing works—“While climbing, […] you lose your Dexterity bonus to AC (if any),” nothing about flat-footed or invisibility.
helpless works−see sleep (which is one way to become helpless).
pinned works, as does any other form of grappling, so long as the sneak attacker isn’t the one doing the grappling—“While you’re grappling, […] You lose your Dexterity bonus to AC (if you have one) against opponents you aren’t grappling. (You can still use it against opponents you are grappling.)” Nothing about flat-footed or invisibility.
Improved Uncanny Dodge
Improved uncanny dodge prevents flanking:
This defense denies another rogue the ability to sneak attack the character by flanking her,
Which both rogues would have.
However, that sentence continues
unless the attacker has at least four more rogue levels than the target does.
Thus, the 20th-level rogue could flank the 15th-level rogue (20 − 15 = 5 ≥ 4), but the 15th-level rogue could not flank the 20th-level rogue (15 −20 = −5 < 4). The 15th-level rogue could still sneak attack the 20th-level rogue, if the 20th-level rogue’s Dexterity bonus was denied to their AC.