So I have noticed that in most of the campaigns I run or play in, no one really makes characters that are designed to work together. Sure there are cooperative feats, but are there any magic items, classes, prestige classes, or any other such thing that makes it more worthwhile to be near a specific person? This is not just a tactics question, but mostly flavor. I'd love to see certain magic items or classes that give each other bonuses from helping one another.
I am not sure if this is exactly what you are looking for, but both me and my melee comrades love telikenetic charge.
Also, I have read about Dragon Clan Cavaliers being outstanding for teamwork.
You're looking for bards and cavaliers. Bards make everyone around them better at everything, and cavaliers can lend their teamwork feat to allies so everybody doesn't need to buy the same feats. All casters can do a good job of buffing their meatshield friends, but the martials don't have many good options for protecting their friends.
If third party is allowed, Rite Publishings Secrets of Tactical Archtypes 1 & 2 are pretty good at giving nearly all the F classes some team boosting ability. Rogue Genius Games Warmaster is a full BAB class entirely based on making the party work together, without the mount baggage of the cavalier. The upcoming Path of War from Dreamscarred Press has at least one disciline entirely focused on helping the party and giving them extra moves and bonuses.
That does sound pretty awesome. I was hoping there'd be something similar to how in the D&D 3.5 book ,Complete Adventurer, Daggerspell Mages and Daggerspell Shifters we made to work together, or even Nightsong Enforcer/Infiltrator. I can't seem to find any PrC's that were made to go together.