If you can get your hands on one at a reasonable cost get the Martial Arts Companion. Even if you don't use Monks/Martial Arts a lot you can use the Fighting Styles to expand your Pure Arms characters capabilities a bit.
If you use Talents/Flaws take a look at Talent Law as it's packed full of them. You also find expanded ones in the Essence, Channeling and Mentalism Companions. You need to eyeball the costs (some are out of whack compared to each other), I have my players go through and selected all the various Talents/Flaws, give me the list, then I price them out for them and they select which they'll actually do then (or just sit down with them and do it).
Also, just to be clear, there are three books that are basically the equivalent of the full blown "Spell Law"
Spell Law... of Essence
Spell Law... of Mentalism
Spell Law... of Channeling
Then there are the 'Companion' versions of those which are different and add the new expanded materials.