Well, I'm pretty sure that everyone in here knows about the Rockets failed efforts to pursue a FA this season (except for Ariza), so I'll skip that part and just go ahead with my post:
Of the few players left in FA, the only "quality" players (which will help the team in some way) which are left are:
Eric Bledsoe
Greg Monroe
Ray Allen
Shawn Marion
Emeka Okafor
Andray Blatche
Jameer Nelson
Aaron Brooks
Jimmer Freddette
Of the group, only Bledsoe and Monroe are restricted free agents, and considering the Suns have all the cap space and willingness to match offers for Bledsoe, Allen's pondering retirement or signing with the Cavs, and my thinking that Aaron Brooks will have some respect for himself and not sign again with the team that traded him last season, the remaining players we could have are:
Monroe, Marion, Okafor, Blatche, Nelson, Freddette.
Of the above only Monroe figures to be a starter, and we have the salary cap to get him at $15 million (which might be overpaying a little bit for him, but that was what Parsons contract is worth). I think that with SVG running the show at Detroit and having Drummond and J. Smith already in the team they would find it hard to match an offer that high for him (Even though SVG has said Monroe is their priority).
But problem is Monroe isn't by any means a stretch-4, he's more of a traditional PF who'll get his points from midrange shots and post ups, so I'm not sure he'll be a great fit in the Rockets system, but he would anyways be an upgrade over Jones.
Okafor would be the perfect backup center now that Asik is gone, he's actually a guy who's career per 36 min are 14 and 11, and he would probably come at a cheap price given he spent all of last season recovering from a back injury.
Marion is a great defender even though he's 36 years old already, but I think that our chances of getting him are low as he wants to go play for a title right now.
Blatche and Nelson would just be nice role players to fortify our bench. I like Freddette because he is a great spot up shooter and would be a great option for Harden to kick out to. But he's undersized and a nightmare defensively, still he would probably come pretty cheap and provide some quality minutes off the bench.