I believe that the title is really explanatory for the question. But let me expand this a little. Can a monk deliver effects that require touch attacks with an unarmed strike?
For example, would a cleric/monk be able to use an unarmed strike attack + damage for an inflict wound spell? And if that is not possible by the PHB rules, are there any feat allowing it?
Please note that by touch attack I only refer to melee touch attacks and not always spells. The actual question popped in my head while reading this: Walker in the Waste prestige class from Sandstorm and its Desiccating Touch ability.
Best Answer
Delivering a spell as part of an unarmed strike
In answer to your question, yes a monk can deliver a touch attack spell through his normal attack. However you have to hit against their normal AC to do so, not their touch AC. If you miss their AC, you fail to do damage and the spell does not fire (even if you miss their AC, but hit their touch AC). If you hit, you do all the normal damage of your attack, and then the spell goes off. That's the advantage and disadvantage of doing it this way. The rules for this are here (thanks to @Tridus for the link).
Delivering a spell as a touch attack using natural weapons
A cleric/monk could also deliver the spell as a normal touch attack, rolling against the opponents touch AC, but doing no damage for his fists. This works no differently from any other touch attack because
You can think of the difference between this and delivering it as part of a normal attack as a normal attack being a full on punch with a spell going off as the punch connects, whereas just going for a touch attack is just tapping the opponent anywhere, not bothering to penetrate their armour, and the spell goes off the moment you make contact with them.
Other classes
There are several other classes that do this type of thing by design, such as the Duskblade, who can deliver spells through their normal attacks. Having a look at the rules for them may give you further insight, if you need any.