Let me preface this by saying, I don't think the Titans will really reach outside of their roster to make any additions this year (except maybe on kicker). However, these are the players that I think could make an immediate impact on the roster.
Kevin Vickerson DL
The Titans already have their two NTs in Sammie Lee Hill and Daquan Jones, however the 5-technique could use some talent and experience. Vickerson is a load to move and he could easily come in and be the second string 5-tech behind Ropati Pitoitua who is dealing with a broken hand.
Vickerson has the nastiness that this defensive line is really missing, which really makes a difference in the running game. As for the Titans level of interest, they definitely haven't shown an aversion to taking former Broncos players. This year the Titans brought in Wesley Woodyard and Shaun Philips, so why not finish the trifecta?
Steven Hiil WR
While some people think Hill is a bust, I just think he is a work in progress. Starting out with the Jets is probably the worst case scenario for a young wide receiver who is viewed as a project coming out of college.
It is hard to argue that there is a better wide receiver coach in the league that Shawn Jefferson. He knows how to get under a young player's skin and make them better. Justin Hunter had a lot of talent coming into the league, but there were a lot of question marks about his ability to make plays all over the field. In just a year Jefferson took Hunter from a player with a limited skill set, to a player possibly on the way to a breakout year.
The Titans have no talented depth at wide receiver, and it would be interesting to see what Steven Hill could look like after a year of great coaching. If he didn't pan out, what would the Titans lose? Derek Hagan? Not exactly a crippling loss.