I would consider a trigger of some kind. Triggers that are known to not have a attitudes are the hawian (that's what I have), niger, blue jaw/throat, pink tail & a few others that I cannot remember their name & Joel has 1-2 in his shop. For a 150g I wouldn't do a hawian but 1 of the other triggers I listed.
Puffers are also a excellent addition. The porcupine & spiny box puffers are 2 of my favorite! Relativly cheap with a awesome personality. The problem with these guys, are certain fish mostly angels like picking on them
There are several other puffers that you can look at which angels & tangs usually do not bother. I just picked up a Mappa puffer for my FO tank.
Pretty much any angel would work (just not with those puffers). My favorites are the emperor & queen angel. They both can get pretty large & might outgrow the 150g.
wrasses are also pretty interesting. LOTS of cool options there.
You can always add a few more tangs - Naso, yellow, purple etc