A Dragon article describes plane shift's forked rods
A list of tuning forks for AD&D for use with the spell plane shift appears in the Dragon #120 (Apr. 1987) article "Plane Speaking: Tuning in to the Outer Planes" (43-4). Names of planes changed with editions, but determining, for example, that D&D 3.5's Carceri is 1987's Tarterus takes only a little research.
The article includes what's needed to to travel to the Material Plane (which at the time was the Prime Material Plane):
Reaching the Prime Material Plane Material Plane requires a steel C-fork. The spell will take the travelers to the Prime Material Plane to which the metal is native. If the metal came from an alternative Prime Material Plane, then the fork will take the traveler to that plane. Such forks are normally used by those interplanar travelers who wish to return to their native plane. (43)
The article describes metals forks must be made of and musical keys forks must be in for many planes, including para- and quasielemental planes and multiple layers of some major planes. (For example, an E-flat tuning fork made of iron is needed to reach Othrys, the first layer of Carceri.) The article excludes demiplanes.
The article's by Jeff Grubb, an old school giant who, in addition to working with Gygax on the AD&D Monster Manual, wrote products such as Spelljammer and TSR's Marvel Super Heroes: The Heroic Role-Playing Game (that is, the original version).
In D&D 3.5 the DM may rule that the plane shift spell's foci must be acquired during the campaign
The 7th-level Sor/Wiz spell plane shift [conj] (PH 262) has the following focus component:
A small, forked metal rod. The size and metal type dictates to which plane of existence or alternate dimension the spell sends the affected creatures. Forked rods keyed to certain planes or dimensions may be difficult to come by, as decided by the DM.
And the Player's Handbook says that
A focus component is a prop of some sort. Unlike a material component, a focus is not consumed when the spell is cast and can be reused. As with material components, the cost for a focus is negligible unless a price is given. Assume that focus components of negligible cost are in your spell component pouch. (174)
However, the Player's Handbook also says that Chapter 11: Spells
begins with the spell lists of the spellcasting classes and the list of cleric domains and the spells associated with each domain. An M or F appearing at the end of a spell’s name in the spell lists denotes a spell with a material or focus component, respectively, that is not normally included in a spell component pouch. (181)
The spell plane shift—both the cleric version and the sorcerer/wizard version—has such an F despite the spell's long description providing no costs for these foci.
So while the spell's long description is very important, and there it's assumed "that focus components of negligible cost are in [a] spell component pouch," the Player's Handbook directs the reader also to the short description that contains potentially new information that's totally unavailable elsewhere.
It's possible—game-legally, anyway—for plane shift's F to be a text-trumps-table issue.1 Yet, unlike many text-trumps-table issues, this issue has actual printed rules informing the reader what these notations mean as separate rules. Nonetheless, the DM must determine if this notation on plane shift is a rule or if this same error has existed through at least the 2000, 2003, and 2012 printings of the Player's Handbook (the ones I own, this last the edition incorporating errata (like to dispel magic's area entry) and stealth-fixing the feat Spring Attack but still not giving the monk unarmed strike proficiency, for instance), because that F follows the spell plane shift on each book's tables.
A DM that assumes this F is an error causes a spell component pouch to include tuning forks for every conceivable plane—including demiplanes like the storage areas of bags of holding and like those created by the 9th-level Sor/Wiz spell genesis [conj] (EL 117)—, and limiting access to some usually obscure planes may be difficult.
A DM that assumes this rule is accurate vastly limits the versatility of the spell plane shift, removing from a spell component pouch all forks for all planes. (For some DMs, this is a good thing). Further, played strictly, this rule has additional implications that resonate throughout the system. For example:
The 7th-level Sor/Wiz spell simulacrum [conj] (PH 279-80) has an M, and simulacrum has the following material components:
The spell is cast over the [creature that's to be simulated's] rough snow or ice form [that's created by the spell], and some piece of the creature to be duplicated (hair, nail, or the like) must be placed inside the snow or ice. Additionally, the spell requires powdered ruby worth 100 gp per HD of the simulacrum to be created. (280)
A DM that strictly follows the F/M spell table rule eliminates all of these material components from a spell component pouch, making it so a spell component pouch no longer contains nails or hair of every creature (including every god) that's ever existed. Whether placing this limit on simulacrum—and, likewise, the 9th-level Sor/Wiz spell ice assassin [conj] (Frostburn 97-8), both among the game's most campaign-changing spells—is a good thing is up to the DM.
The 8th-level Sor/Wiz spell binding [ench] (PH 204-5) has an M, the binding spell's material components being
In addition to the specially made props suited to the specific type of binding (cost 500 gp), the spell requires opals worth at least 500 gp for each HD of the target and a vellum depiction or carved statuette of the subject to be captured. (205)
A DM that strictly follows the F/M spell table rule eliminates from a spell component pouch vellum depictions or carved statuettes of every creature (and god!)—known and unknown—since the dawn of creation, despite these items having no listed costs. While the spell binding lacks the long-term campaign impact of simulacrum (except for the hilarity of preserving important advisory heads in jars a la Futurama through the metamorphosis version of binding), allowing everyone who can pay 5 gp to possess a sketch or pewter miniature of every creature ever (including itself) would, I think, strain verisimilitude even in a high-magic setting.2
Obviously, it's perfectly reasonable to develop a compromise between these two extremes; for example, a particular campaign's spell component pouch could contain common tuning forks, hairs and nails of common creatures, and drawings of common creatures, but exclude foci and material components involving rare, weird, and unique planes and creatures. It's a game, after all. Have fun.
While the cost may be negligible for plane shift's tuning forks, this DM believes that the forks probably shouldn't be included in a spell component pouch, and that the Player's Handbook's Fs (and, therefore, Ms) are accurate. This DM, however, has a house rule that says a spell component pouch contains a tuning fork appropriate for the pouch's plane of manufacture (i.e. a spell component pouch made on the Material Plane contains a Material Plane tuning fork). A more generous DM might include along with the pouch a dozen or more forks, and a less generous one that wanted to thoroughly restrict planar travel may make every fork a quest.3
1 "When you find a disagreement between two D&D rules sources, unless an official errata file says otherwise, the primary source is correct. One example of a primary/secondary source is text taking precedence over a table entry. An individual spell description takes precedence when the short description in the beginning of the spells chapter disagrees" (PH v3.5 Errata 1).
2 I mean, really, who makes all those?
3 Pro Tip: In such a campaign, find the Material Plane fork first!
Note: Insomniac's deleted answer (visible to those with sufficient reputation) was integral for composing this answer.