My last campaign was a disaster because I had TOO many house rules. It became unmanagable.
Of the few houses rules I have in play, the ones that pop in my mind ATM are
- Wizards and Sorcerers can forego the familiar in exchange for an arcane Feat of their choice. (this one is very popular)
- Whenever the game pauses as a result of confusion over whether a creature could get an attack of opportunity or not, it doesn't.

I've never mentioned this rule to my players, and since none of us can keep track of when/if/how attacks of opportunity occur EXACTLY, I just use the "group stumped" method of decided then and there that it doesn't.
- Max hit points at first level
- I use "common sense" rules with regards to multi-classing and PrC advancement. I denied the bard the ability to multi-class to Cloistered Cleric (UA) solely because he wanted to get the
identify spell for free. Now, I would have allowed him to add a level of cleric if he were pious, but he wasn't. His character didn't know the first thing about the tenets of his deity.
And of course, I use the
Artificer's Handbook for item creation. But, no one is interested in item creation, so it doesn't come up very often. I do use it to add quirks to items, and for the potion flavor/color chart. Be aware that if you do use this book, you need to sort of make a decision regarding the multitude of optional rules that are peppered throughout the book. Like, whether to give "scribe scroll" to wizards for free, or to make it a separate feat, and exactly which method of scribing a scroll you want, and the breakpoint level for instability in your world (if you use those rules).