Infinite Wish Loop

It kind of goes like this. Bonus round: Can you discover the highly exploitable flaw in this man's wishes splorks? (1st guess: "Splork" is cartoonish sound effect for being squashed - so, "I splork for infinite splorks" is "I squash for infinite squashes", definitely not what he intended)

"I will grant you three wishes, but no wishing for more wishes."
"Gosh, I wish I could wish for more wishes."
"... fuck."

Role-playing games with powerful wizards usually have a spell called "Wish" or similar at the top tier of spellcasting, and it's supposed to be the wildcard of do-as-thou-wilt magical effect. But any DM knows the problem with giving players a blank check: they're going to actually try to cash it in. If the game wasn't written by a noob, the spell description for the Wish spell will have specific limits on what can be wished for, including "No wishing for more wishes!" and "No wishing for more beings who grant you wishes" in order to prevent cheesing via infinite wish loops.

...Ha ha, screw that. The Wish spell is supposed to be an "I win" button, and we're going to win the fuck out of this game. This page should be a list of how to get nigh-limitless uses of the Wish-type spell effect in games.

Wishing for more Genies

A system generic option, the ploy of 'Wishing for more Genies' exploits the fact that though the number of wishes is limited, there is no rule that limits you for wishing for more objects to grant wishes. Other proposed workarounds also exist, but it's another story entirely.

Candle of Invocation Loop

The D&D 3e version of "Wishing for more Genies" is the Candle of Invocation Loop. Step 1) Get a Candle of Invocation (8,400gp, could show up in the treasure for encounter level 12). If the Candle matches your alignment, you can use its gate feature. The Candle has caster level (CL) 17, so you can use the Candle to gate in 34 hitdice of creatures, and have them serve you immediately for 17 rounds without needing payment. This will destroy the candle, but no worries.

Gate in an efreet (10 hitdice). Among its spell-like abilities is "1/day grant up to three wishes (to non-genies only)". Wish one: Ale. Wish two: Whores. Wish three: another Candle of Invocation of matching alignment, pretty please (or just 3 Candles of Invocation). Cheese aficionados should recognize this method as a crucial step of the early versions of the Path to Pun-Pun. Newer versions bypass this by exploiting that Pazuzu grants Paladins one free, uncorrupted wish to tempt them. In fact, since the Candle can gate in 34 hitdice of creatures, you can gate in 3 Efreets (30 hitdice total), for total of 9 wishes (since you don't need a particular individual Efreet; and using bigger Efreet doesn't increase his wishes amount). Since Efreet casts as spell-like ability, all material and XP costs are null.

You could also kick-start this loop if you cast Gate directly. It is a level 9 spell of Cleric, Sorcerer, Wizard, and "Glory Domain" user, and costs 1000 XP; so, it would require a relatively high-level PC to work that way (you need 17 Cleric/Wizard or 18 Sorcerer level to cast Gate directly). Candle Of Invocation, however, can be used by anyone and can be bought as early as 5th level if you have proper wealth-by level (possibly even earlier if we pool all PCs' funds).

You could also summon gods, deities, and similar powerful entities with Gate. While they can't be controlled, and get summoned only if they want to (ask them before casting Gate — or better yet, ask all gods to notify you when they want to be summoned) — they're incredibly powerful, and Good god would still do good things even when he's uncontrolled. Sometimes, their time may be limited due to them having some kind of mind-bogglingly important things to do at their plane of existence — but, a god can do more in a round than a PC could do in a year (and they should at least have the "time available without need of payment" amount of rounds available for local affairs).

Wand Surge

This one's for D&D's Eberron setting. Your character should have the 'Wand Surge' feat, and you've hopefully acquired a Wand of Unfettered Heroism with at least one charge left (or can just cast it yourself, but that takes too long). If you have, then get yourself a Staff of Wishes with at least one charge left.

Zap yourself with the wand, which gives you a free action point every round for one minute. Use that action point every round with the Wand Surge feat to use a magic item without expending a charge. One minute = 10 rounds, so that's ten uses of the Staff of Wishes without expending the last charge. You can wish for more Staffs of Wishes.

Chain of Simulacra

The exploit of choice in 5th edition D&D involves the Simulacrum spell, which allows you to create a clone of yourself (or any other character) that has the original's spells and spell slots. Including Wish. This lets players get around that pesky "Casting Wish means you have a 1/3 chance of never being able to use it again" restriction, because it isn't the player who is casting the spell. This is also used to create an ever-expanding army of 17th level spellcasters, as the Simulacrum can cast its one use of Wish (simulacrum spell slots don't regenerate) to make another Simulacrum, and that one spends its slot to make another, until… until nothing, because this train will not stop, and has no reason to stop. You won D&D, good job. I hope you're happy.

3E has a variant based on duplicating a monster with a Wish SLA, and using the wish to duplicate simulacrum. Mirror Mephit, a stupidly easy to summon monster with a Simulacrum SLA, is a popular starting point.

This can also be used to implement the Peasant Railgun, if you really wanted to.

Music Beyond The Spheres

The Pathfinder Bard masterpiece Music Beyond The Spheres manages to loop Limited Wish with itself as long as your bardic performance rounds (which can easily be 35+ in a day by the time you first get this, and each wish only costs one round) lasts. The masterpiece duplicates Limited Wish at the cost of con or wis drain instead of the diamonds. The spell Restoration, which Limited Wish can duplicate at no extra cost, removes all ability drain. This means you can cast 9+ limited wishes for whatever, then another to cast Restoration and remove the drain you incurred.

9 Limited Wishes can generate 27000GP of stuff (Duplicate Fabricate with 1000GP free material components for 3000GP) and then a 10th can fuse it into a single technological item. This can then be sacrificed to cast a real wish with Music Beyond the Spheres.

Painting Power

In Painting Power, it's explained how to effectively go to god power levels at level 5. Using painted Efreeti for an infinite wishes loop there is the LEAST broken part; just go and read it.

Discounted Wishes

For cases when methods above get banned. Cast Gate, summon as much Efreeti as possible, use their Wishes as needed. While it's not "true" infinite wishes, it's still better than casting Wish directly; you only pay 1000 XP, don't pay extra XP to make magic items or duplicate spells, don't pay any material components, get about from 3 to 9 wishes for a single cast (you can call multiple Efreeti per Gate cast), don't risk "being unable to cast Wish ever again", and can also do this as Cleric/Glory Domain User.

Wish Creating Wish-Making Magic Items

Alternate route. You start with Wish, what doesn't use XP and doesn't have chance to "never be used again" - i.e. usually casted by summoned Efreeti or magic item. You use that Wish for Wish-casting magic item with multiple charges (like Staff Of Wishes). Keep Wishing for more Wish-making items. Now you have functional infinite wishes loop.