Interesting that nobody mentioned (that I remember seeing) the Spontaneous Metamagic (specifically the Daily Uses part on pg. 152). I love the rule personally and have already applied it to our campaigns, but haven't really gotten any dedicated spellcasters at high enough levels to make use of metamagic feats. Therefore, it sounds great for me, but I can't say that it's balanced or not by experience. I've added a house rule to this where a character can take a metamagic feat multiple times to reduce the spell level adjustment by one for three castings per day. So you can take Quicken Spell twice for a +3 spell level adjustment, 3 times per day, or twice for a +4 level adjustment, 6 times per day.
I've also used to good effect several class variants and LA buyback. Would love to try the weapon group stuff if I can get my group on board with it. Not much else has been tried at this point.