I like that Steve Nash was mentioned, not conventionally tough but bloody him up and he'll come right back out twice as hard as before.
Can't believe no one's said Pierce though. Life-threatening condition, was told it was a huge risk coming back so early, and what does he do? Drops 28.
Matt Barnes probably isn't all that tough but deserves to be in conversation just because I've never seen anybody get so involved with Kobe (possibly the toughest) for an entire game like that.
Gotta give Andre Miller a shout out, played in 632 consecutive games until he got suspended for throwing a guy way bigger and more athletic (Griffin) 5 feet like a rag doll.
Edit: Guys like Blair should get credit too for being a force despite their size. Don't underestimate what it's like to be under the basket in the NBA, never mind with guys that tower over you (Wallace was easily the toughest guy for the entire last decade, head and shoulders above anyone else).