Side Deck (Current March 1, 2012 Ban List)

Here is a list of cards that is advisable to put in your side deck.
This is just general cards that are advised in a side deck. These cards are not, and shouldn't be, considered must-have in every side deck. Sometime, certain cards are better sided, depending on the deck.

Card	Amount	Reason
Cyber Dragon/ Chimeratech Fortress Dragon	2/1	Against any Machine deck, this card can destroy, since it can take your opponent's monsters for the fusion and it gains 1000 ATK for every material used. This this card is best against Karakuri or any other Machine deck, where your opponent will probably be spamming a lot machine types. Also effective on Wind-up Zenmaines, since it doesn't destroy it, they lose their blocker and all the effort making it (Which is often just a Tour Guide of the Underworld and another one or a Sangan.)
Snowman Eater	1-2	Snowman Eater, when flipped faced-up (note: it's not a FLIP effect) you can blow up a monster. Now it may seem like another Man-Eater Bug, but Snowman Eater is sitting pretty with 1900 DEF. Pretty much, this mean he can withstand Thunder King, Tengu, and most early drop monsters AND get rid of them; netting you advantage on the field.
D.D. Crow	2	If you discard D.D. Crow, you can banish a card in your opponent's grave. This helps stop Plants, Junk plays, Pot of Avarice, and anything that targets something in the grave, even Reborn.
Wattsquirrel	1-2	Wattsquirrel negates the effects of anything it battles with, even when it hits the grave, and it can attack twice. At first glance, this isn't too major, since Wattsquirrel itself is quite weak, but their effects are negated as long it is faced-up or even in the graveyard (Treeborn Frog and Sangan) and since it can attack twice, you can hit two monsters to stop a lot of effects, assuming Wattsquirrel survives the first one and you are willing to take quite a bit of damage. You can always just set it though.
Dimensional Fissure	2	This card is pretty much the continous spell version of Macro Cosmos (so see futher down for more on RFGing and how it hurts decks). This ruins many decks as Remove from Play is often something many decks cannot hold up against. The reason you would run two of these along with a set of Macro Cosmos is to help consistency and to be able to draw one or the other more often so you can hassle your oppenent more and more.
Nobleman of Crossout	2	This card HATES on Gravekeeper Spy's and Ryko's, since gravekeepers are still about and Ryko is more abundant with Chaos and Lightsworns running about. One it hits a Spy or Ryko or any other FLIP monster, Nobleman bainshes the rest from BOTH players decks and graveyards, which shouldn't bother you unless you're mirror matching and you hit something you yourself have in your deck. But you wouldn't be siding this in if you were mirror matching would you?
System Down	1-2	This card helps against many different types of machine decks, like Karakuri's. 1000 life points is well worth removing all Machines on the field and graveyard. Gets rid of machine synchros and anything else that's big or anything they can fetch in the graveyard (like Karakuri Ninja Kuick). Also bypasses Stardust Dragon and Starlight Road since it doesn't destroy anything. AND it also only removes on your opponent's field and graveyard, so it doesn't hurt you if you are running a machine deck.
Extra Gate	2	An odd ball but a personal favorite, Extra Gate allows you to choose a Level 1-12 and your oppenent banishes one synchro of that Level from their extra deck. If they have none of that Level, you discard a card. Although it doesn't hit XYZs (which is a shame) it does hit key pieces in synchro decks. Call Level 2 to hit Formula Synchron or call Level 12 to hit good old Shooting Quasar Dragon. You can also call things inbetween to help weed out Level 5's and Level 8's that we all hate (Scrap Dragon, T. G. Hyper Librarian, to name two). However, the flaw is that your OPPENENT chooses so if they have more, they might throw out a filler or something useless (Gaia Knight, The Force of Earth or a Magical Android) and also, if you do happen to call it wrong or if they already used them all up and you forgot/didn't know and still called it, you have to still discard that card, which may suck at key moments.
Shadow-Imprisoning Mirror	2-3	Gravekeepers. Inzektors. Diamond Dude. This card really helps stops that derp. However, be wary of the amount of darks in your own deck. You could be hurting yourself with this card.
Bottomless Trap Hole	2 (semi-limited)	Despite having warning floating about and Bottomless's 1500 more requirement, Bottomless is not that bad. It's free to play in terms of life points, removes it from play, and take out multiple number of monsters that are summoned at the same time (Rabbit). Now if only we didn't have priority anymore. This card would really shine better. Now without priority, this card can hit all those things that annoy us so, (Black Luster Soldier - Envoy of the Beginning and Judgement Dragon to name two). Also, this can be Main Decked now without too much concern. Although Solemn Warning still hits more cards more effectively (they never hit field), it still costs 2000 Life Points to play.
Imperial Iron Wall	1-2	This card stops cards from being banished. Stops Fusion Gate HEROs and any thing that needs to remove in order for their cost (Black Luster Solider-EotB) or effects to work (some Lavals)
Macro Cosmos	2-3	This card removes any card sent to the graveyard out of play instead. Macro Cosmos helps stop things that need to activate in grave (Stardust Dragon cause he can't re-special himself, Sangan, Giant Rat, to name a few) or things that need to be discarded or sent to the graveyard (Namely Effect Veiler) so it's very useful against many different decks. However, it is not for everyone. If your deck is a deck that is hurt by Macro Cosmos, you shouldn't side it. Also, if you DO happen to run Helios - The Primordial Sun, if you special Helios - The Primordial Sun from Macro Cosmos's second effect, this card CAN be warning'ed (like Starlight Road).

Work In Progress.

This list will be updated as things change about the meta scene. If you have any input or things I missed, comment and I will add them.

Update 1/16/2012 2:58 am
Added more and expanded on ones already posted
Update 5/31/2012 8:00 pm
Added more, removed outdated, updated.
Leeching no longer viable due to Lightsworns and Twilight dropping out of favor.

System down: This card is great against Karakuri or other machine decks.

Imperial Iron Wall: I like to side this against Fusion Gate Heros. It stops their gate plays and stalls them for a while :3 Not the best thing to side but pretty trollish if done so..

Leeching the Light: This card is pretty good against Agents and the various other light attribute decks.

Watt Squirrel: This card saw some side deck action a couple YCS' ago and can still be used to surprise some Plant players etc......

Snowman Eater: Some people have used this card against Rabbit decks to bounce the Laggia, etc... It also spars with Rai-oh and bounces him

thats all I have for today~

Snowman Eater actually blows stuff up, not bounces.
And good ones, I forgot about system down, probably cause machines haven't been to rampant (aside from Karakuris) and for some reason system down has never been brought up as a side for them, at least I haven't heard.

hm....the side seems to be updated! What seems to be the to tier?
Rabbit
Inzektor
Wind-up
Lightsworn (Theres a lot of hype right now)

Yeah they seem to be, any ideas?

I got none really...