Okay, this is quite possibly the coolest and single most useful section in the DMG (as well as competing for the most expansive). WotC could really take a lesson from this section, as the third edition DMG is sorely lacking in this information, which has been replaced by reams of notes on tactical square-based miniatures combat.
Our section begins with a chart of "Standard Hirelings, daily and monthly costs," followed by a brief writeup of what each hireling is and does. These are your basic shopkeeps, tradesmen, etc, such as carpenters, torchbearers, tailors, teamsters, masons, porters, etc. that can be found in pretty much any village or town. A few brief examples of services provided and how long they take follows.
After this section, we get into the real fun...
Expert Hirelings: These are the guys you seek out in large towns and cities who are sought-after experts in their field. Here we have architects, mercenaries (of every shape, variety, and classification), spies, ship crews, scribes, and the ever-so-useful sage. Following the introduction, each type of expert hireling gets a few paragraphs and charts covering the length of time to accomplish common tasks, the cost to do so, and the types of services each can provide. The expert hirelings here covered are:
Alchemist, Armorer, Blacksmith, Engineer (architect, artillerist, sapper/miner), Jeweler-Gemcutter, Mercenary soldier (archer-long and shortbow, artillerist, captain, crossbowman, footman--heavy, light, pikeman, hobilar--heavy and light, horseman--archer, crossbowman, heavy, light, and medium, lieutenant, sapper/miner, serjeant, slinger), sage, scribe, ship crew, ship master, spy, stewerd/castellan, and weapon maker.
After three pages of description of each and every one of these babies, up through the mercenaries (and at that small 7 point font), we get to a massive section on sages.
Sages in 3.x are pretty much left to the DM to figure out on his own. They're experts; just treat them that way and roll with it. Not so, here. Here we have a detailed breakdown of sage abilities, their major and minor fields, and special categories in their major fields. These are represented by loads of charts, combining the nature of knowledge with the chances of knowing the answer to a given question, and how long it will take the sage to research that question (and the commensurate costs to do so) if he doesn't know the answer.
We are given a section for determining the alignment, special skills, and other characteristics of the sage in question, followed by bits on locating, hiring, and employing a sage both short- and long-term. It even discusses how much rest and recuperation a sage will need after throwing himself into extensive research mode.
Make no mistake; if your players decide to have their PCs consult a sage, and you have not already designed an NPC for that purpose you want this section handy. Everything you need right at your fingertips; a fully fleshed-out sage can be whipped up in 2 minutes flat with what's here.
After the sage section, we finish off the Hirelings section with the rest of the alphabetical list. While just as comprehensive as the pre-sage entries, after the kind of information we got regarding sages, suddenly it seems a bit less cool. But still, incredibly useful information that has been criminally overlooked in later editions of the game.