There are many possible things you can wish for. This page attempts to list the most important ones.

See also What not to wish for.

All-game wishes[]

Text to wish for Why choose this wish? Notes
Seven league boots Blessed seven league boots reduce the energy cost for movement from 1000 to 750. This allows the PC to move faster than almost all monsters. Only one pair can be gained per wish.
Spellbooks of Acid Ball Acid Ball ignores magic resistance, and there are few monsters immune to acid damage. It's a powerful spell in general and one of the easier ways to deal with Nuurag-Vaarn. Priests, Paladins, Druids, and Chaos Knights should ask for "spellbooks of Rain of Sorrow".
Concentration The Concentration skill is almost essential for spellcasting, and definitely worth a wish if you plan to use magic.
Find weakness The Find weakness skill increases your chance of critical hits, making it useful to all melee-oriented PCs without good slaying weapons.
Rings of regeneration, pairs of bracers of regeneration, crowns of regeneration Magic regeneration allows the PC to recover 1 HP per turn per regenerating item. Among these items, rings are typically a better choice, as two of them can be equipped simultaneously, and they are less likely to be destroyed if the PC has gauntlets equipped.
Potions of toughness Increasing Toughness improves survivability. Only two can be gained per wish. For PCs with low toughness, wishing for potions of potential toughness and using morgia roots may be more effective.
Staff of purification Given enough patience, it can deal with all corruption except for Mana battery. Only one can be gained per wish.

Early game wishes[]

Text to wish for Why choose this wish? Notes
Tower eternium shields Eternium tower shields are the best non-artifact shields in the game.
Red dragon scale mails Red dragon scale mail increases PV by +13, as well as granting fire immunity, making it a very powerful piece of armor. Eternium full plate armors provide more PV, in case fire immunity isn't needed.
Amulet of life saving Giving an AoLS to Khelevaster is the only way to save his life; which opens the option of an Ultra ending while also granting you many scrolls of corruption removal. Only one AoLS can be obtained per wish.

Mid game wishes[]

Text to wish for Why choose this wish? Notes
Rings of ice Rings of ice protect worn equipment from fire damage, very important in the Tower of Eternal Flames. They are relatively less important in other areas of the game, and not worth a wish.
Fireproof blankets Fireproof blankets protect your inventory from fire damage, which is always useful. They can be useful when attempting the Tower of Eternal Flames, but their wish-worthiness is debatable.
Alchemy Alchemical explosions can obliterate pretty much anything that isn't immune to fire. The explosions hit the PC, so fire resistance or immunity combined with some form of fireproofing to protect items is advisable.
Emperor moloch A wish for the emperor moloch will grant ~30 greater molochs, assuming the emperor has not already been slain. These can be killed for a LOT of XP, if the right tactic is used. This is a VERY dangerous wish to the unprepared.
Banshee A banshee can clear the bug temple relatively safely, if the right precautions are taken (see here). The rewards include three scrolls of corruption removal, a pile of 12 quarrels of slaying, 6 potions of ultra healing and a padded elven chain mail of resilience (great for Monks), among others. This is a VERY dangerous wish to the unprepared.

Late game wishes[]

Text to wish for Why choose this wish? Notes
Speed It provides a huge, temporary boost to speed, usually making any difficult fight much easier.
Potions of uselessness One can be exchanged for a random artifact on D:49.
Potions of quickling blood Speed is always useful, and these potions provide permanent increases. More of a luxury wish.
Girdle of giant strength Greatly increases Strength. More of a luxury wish. Only one can be gained per wish.
Magical writing sets Can be used to write useful scrolls, such as scrolls of education or scrolls of corruption removal. Scrolls of defense/protection are worth considering too to improve non-metallic items. See the item page for detailed considerations for scroll writing.