Consider the section of the rules called "Touch Spells in Combat." You can find them here for Pathfinder. They are scattered across this page in D&D Third Edition; search for "touch" to find them.. Both sets of rules are essentially identical, but the Pathfinder version is written more clearly. Here they are:
Touch Spells in Combat: Many spells have a range of touch. To use these spells, you cast the spell and then touch the subject. In the same round that you cast the spell, you may also touch (or attempt to touch) as a free action. You may take your move before casting the spell, after touching the target, or between casting the spell and touching the target. You can automatically touch one friend or use the spell on yourself, but to touch an opponent, you must succeed on an attack roll.
Touch Attacks: Touching an opponent with a touch spell is considered to be an armed attack and therefore does not provoke attacks of opportunity. The act of casting a spell, however, does provoke an attack of opportunity. Touch attacks come in two types: melee touch attacks and ranged touch attacks. You can score critical hits with either type of attack as long as the spell deals damage. Your opponent's AC against a touch attack does not include any armor bonus, shield bonus, or natural armor bonus. His size modifier, Dexterity modifier, and deflection bonus (if any) all apply normally.
Holding the Charge: If you don't discharge the spell in the round when you cast the spell, you can hold the charge indefinitely. You can continue to make touch attacks round after round. If you touch anything or anyone while holding a charge, even unintentionally, the spell discharges. If you cast another spell, the touch spell dissipates. You can touch one friend as a standard action or up to six friends as a full-round action. Alternatively, you may make a normal unarmed attack (or an attack with a natural weapon) while holding a charge. In this case, you aren't considered armed and you provoke attacks of opportunity as normal for the attack. If your unarmed attack or natural weapon attack normally doesn't provoke attacks of opportunity, neither does this attack. If the attack hits, you deal normal damage for your unarmed attack or natural weapon and the spell discharges. If the attack misses, you are still holding the charge.
Per the rules, in the same round that you cast a touch spell, you also gain a melee touch attack to deliver the spell as a free action. You get ONE free action to deliver a touch in the same round that you cast the spell. It's significant that delivering a touch attack is a free action, because that means you can use it when it is not your turn to deliver an Attack of Opportunity.
On subsequent rounds, you are "holding the charge." On these subsequent rounds, you can make melee touch attacks to deliver the charge.
Also keep in mind that melee touch attacks deliver double damage with a critical hit (threatening on a 20) and can be used to make sneak attacks as well. The arcane trickster with touch attacks can be an effective combination, especially with a high dexterity and the Weapon Finesse feat.
How many of these melee touch attacks can you make in a single round if you are holding the charge? The rules say, "Touching an opponent with a touch spell is considered to be an armed attack" That means, just like all other armed attacks, you can make one armed attack as a standard action, or as many iterative attacks as your BAB allows as a full round action. Normally this only matters if you miss; because if you hit, the spell discharges and you do not get any more, so more chances to attack are moot.
But that's not always true for a very few special spells, most notably Chill Touch (PF link and D&D3E link), which specifically allows multiple touches. Produce Flame (PF link and D&D3E link) is similar.
A caster with a Produce Flame or Chill Touch spell who is holding the charge and has a BAB +6, say, could make two melee touch attacks with a full action, one at +6 and one at +1. If the caster were subject to a Haste spell or similar magic, then they could make three touch attacks, at +6/+6/+1.
In the case of a wizard casting a Quickened Chill Touch, I would allow the wizard, per the rules, to cast the spell as a swift action, make a touch in the same round as a free action (as explicitly allowed) and then to deliver another touch as a standard action or iterative touches with sufficiently high BAB as a full round action.
In a highly unusual but plausible scenario, a caster holding the charge and making a Whirlwind Attack could deliver a Chill Touch to every foe in reach. In Pathfinder, such would be most effective for an aberrant bloodline sorcerer with an enlarge person spell and the Lunge feat to boost melee touch range from the usual 5 ft to 20 ft. Odds are you would have to worry about running out of touches before running out of targets.
The same situation applies with the Produce Flame spell, but note that an extended Produce Flame actually delivers twice as many touches per spell since the number of touches granted by Produce Flame is dependent on duration.
ALSO note that you do not have to deliver touch spells as melee touch attacks! Per the rules above, you can deliver a touch spell as part of a natural or unarmed attack. Therefore, if you are a monk / wizard, you can cast Chill Touch and then hold the charge. Follow that by a flurry, and every successful unarmed attack you make also delivers a chill touch. Unsuccessful unarmed attacks do not waste uses of the spell!
There is a question about natural attacks. Does an druid in giant octopus form out of water casting produce flame get to make a produce flame attack with each and every tentacle? Or just with the one tentacle that has the produce flame? The jury is out on that one. A form with just one attack, such as a wolf, is no problem. Even the octopus is no problem if you agree that only one tentacle can delver the touch attacks!
Also, if you go for the splat books and third party options, there are classes that allow you to deliver touch spells through a weapon. The Woldian Weapon Mage comes to mind, as does the Pathfinder Magus.
As far as Spectral Hand, note that the spell specifically says, "attacking with the hand counts normally as an attack" -- and therefore you can make one attack as a standard action or iterative attacks as a full round action.
And remember friends, appropriate touching only!