SpringsBoundlessThorns has posted like, all of the familiars on RPGnet. If you like these, then look forward to this Monday when Dragon introduces even more familiars to the mix.
First, feats. You need to take Arcane Familiar to get one, and you can apparently take the feat more than once to give it a defense bonus.
Bonded Familiar allows you to communicate via telepathy.
Shielding Familiar grants you a Reflex bonus while your familiar is passive, and you can destroy your familiar to reduce the damage from an attack that hits you.
Spellseer Familiar grants you a bonus to attacks against creatures next to your familiar and lets you reroll a missed arcane attack once per day.
I like these because these are feats I'd actually want to take. 3rd Edition had some minor feat trees for familiars, but were generally far too underpowered to make it worth your while. I can see many arcanists picking up at least Spellseer Familiar just for the reroll. I mean, I'd even consider Shielding Familiar for the Reflex boost and ability to take half damage from an attack. Those are pretty cool.
Bats have blindsight, can fly, grant you +2 on Perception and Stealth, and can remove concealment from enemies adjacent to them.
The book imp flies, grants a bonus to Arcana and History, helps you understand Infernal, grants fire resistance, and it can turn invisible until the end of your next turn. I really wanted a bat familiar just to irk Adrian, but this seems perfect for a fire-based tiefling. Le sigh...
Cats can have vestigial wings as a quick (see below).
A craft homunculus not only turns enemies into statues, but also imposes a penalty to use alchemical items and is itself immune to them.
Dragonlings can fly, give you Draconic, grant bonus hit points with a healing surge usage, and it can use a breath attack.
Falcons can fly, grant a bonus to Perception and against opportunity attacks, let you determine range from their position once per encounter, and can go twice as far from you as normal.
Owls have low-light vision, fly, add a variable bonus to Insight checks, and you can see through its eyes as a standard action.
Rats grant a bonus to Stealth, can carry objects up to 2 lbs., and can make Thievery checks with a +2 bonus! Thats fucking rad. Also, they get a +5 to Stealth.
Serpents grant a bonus to Bluff, let you ignore a difficult terrain space for shifting, and they can stop all adjacent creatures from making opportunity attacks for a turn.
Spiders can climb, grant a bonus to Athetics for climbing purposes, impose a penalty to saves against immobilize and slow conditions, and can slide an object within 5 squares 2 squares as long as it doesnt weigh more than 5 lbs.
Ravens can fly, grant a big Perception bonus to find hidden stuff, and can speak any language you know. They can converse with other creatures, and you can hear everything it says and also dictate what it says. Interesting.
Now, these are much, much better than their 3rd Edition counterparts, which were almost entirely character dressing that didnt do much except perform as a Tiny-sized XP writeoff. They couldnt really do much of anything because they were too stupid until you hit a certain level, and honestly you were probably better off just not taking one until higher level because they instantly got all the cool shit. That is, assuming you didnt prestige-out into something actually useful, like elemental savant or mage of the arcane order, of course.
I have a couple arcane characters right now, and I'm going to give a bat to my tiefling cunning bard, and probably a book imp to my tiefling summoner wizard.
Quirks are suggestions for various familiars to make them more interesting, I suppose. SpringsBoundlessThorns didnt really go into detail on this. There is apparently a section on how your familiar changes from passive to active mode (appearing in a puff of smoke, changing from a stone statue to flesh, etc).
Familiars cannot be attacked unless they are in active mode. This makes it a lot easier to manage them in 3E where it was possible for t hem to randomly die due to an area attack unless your DM was kind and/or forgot that they were even there.
They only got 1 hit point, basically functioning as a minion. If they die, they dont hurt you in any way, and reform after a short/extended rest. They arent magically treated animals: they are "mystic energy given form", which sounds a lot more thematic and interesting than before.