This thread wins. Smashboards should have a massive youtube series with all of this stuff in it.
And the kitty is hidden in the little ice.. lodge, cabin, house... thing.
The best way to gimp a snake C4 recovery is often a simple footstool, don't underestimate that.
Snake can C4 the sides of battlefield, and many other stages, underneath the ledges, by tapping away from the ledge, and then, while holding down, jumping and pressing b at the right time.
If you are meteor smashed and press the jump button too early, you will receive an additional frame penalty before you can jump, similar to teching too early. However, using your up+b or tap jump avoids this penalty.
You can use a Z attack (i.e. samus') from a ledgehop by dropping, jumping, and the buffering an airdodge to Z and moving onto the stage: this reaches very far.
You can recover from samus' down+b on the ground faster if you hold down till you touch the ground.
ZSS' down+b kick, (performed by pressing A during a flipjump) can be aimed either right or left by holding the desired direction when pressing A.
Not sure if someone said this one already, but I'll say it anways; ZSS can cancel the ending lag of her down+b kick by landing on the very egde of a platform and aiming her kick off of the edge. If you perform either her >100% or <100% ledge attack (not sure which) from either ledge on battlefield, you're perfectly setup to cancel her down+b kick twice in a row on the platforms above if timed right.
Kirby can slam opponents on the top of the columns on either side of Shadow Moses Island by facing away from the columns right next to them, and then using his up throw.
He can also spike Sheik and Lucario off the right ledge of Spear Pillar (the lower ledge) and Pokemon Stadium (1 or 2? Forgot which) using the same technique for the Shadow Moses Island trick, just up against the ledge. I believe metaknight can do something similar with his uthrow.
On the tip of yoshi's nuetral b is a sourspot that simply sucks the opponent right in front of you, but doesn't swallow them, allowing you to grab release wolf off a ledge, and then fall after him and sourspot a nuetral b, pushing him down and under.
Certain fast-fall dair moves give you no lag upon landing if you perform them from certain heights (somewhere above or around a full hop to a midair jump).
Yoshi's down+b, Bowser's down+b, and maybe a few other moves (any dairs?) can be ledge canceled.
Tether recoveries (at least sheik's and samus') can be canceled from a ledge grab by tapping away from the ledge during or during the grab. (Don't forget you only have 3 before you need to land onstage.)
R.O.B. can achieve a greater height with his up+b if you press up+b once, then let go of up, and quickly tap b.
Diddy can launch his rocket barrels (from his up+b) by performing a running up+b into an enemy's banana (assuming you lost one.)
Ganon, falcon, mario, and probably a few others can extend their f-smash by smashing (best done using the c-stick) backwards. If you tap back before smashing forwards, you move forward before the f-smash. You can extend this further by dashing forward and very quickly tapping back again, and finally f-smashing forward for a nice surprise in distance.
Pikachu's d smash, R.O.B.'s d smash, and possibly a few other d-smash moves are incredibly easy to get out of by pushing the control stick up and then rotating it back and forth between the top 3 notches. (Each time you hit a new notch the game reads a new input).
A lot of those are fairly well-known by now, but I got carried away, so whatever.