After December 15 passed, most of the players who were signed over the course of the offseason were officially able to be traded, and a few of the guys who picked up new contracts in that time period should already be on the block.
Of course, there are a handful of guys who have yet to become trade eligible, as any player who was signed after their original team used the league's amnesty provision on them will have to wait until January 15 to become trade eligible.
There are a few other restrictions involving players who just became eligible for Bird Rights (like J.J. Hickson and Eric Gordon) and can veto trades, but that's about the extent of the restrictions for the time being.
For the guys on the trade blocks, there are a handful of teams looking for long-range shooters and defenders if they can be had at the right price. It seems to be a rather weak group of players likely to be on the move at this point, however.
There are definitely some other guys who could be on the move given a few more developments, but for the time being, these six guys look like players their teams want to get rid of the most. The market will dictate whether they end up getting traded.