Rex Ryan,Doug Whaley

Rex Ryan, left, addresses the media alongside general manager Doug Whaley, right, during an NFL football news conference where he was introduced as the new head coach of the Buffalo Bills, Wednesday, Jan. 14, 2015, in Orchard Park, N.Y. (AP Photo/Bill Wippert)

(Bill Wippert)

Orchard Park, N.Y. — The Buffalo Bills took a measured but aggressive approach to NFL free agency and added plenty of talent to an offense that ranked near the bottom of the league in most categories a year ago.

But because of the nature of free agency, coach Rex Ryan and general manager Doug Whaley are still left with a few holes to fill on the roster, and the two biggest team needs heading into March are still areas of weakness for Buffalo.

Let's take a look at who the Bills have added, who they've lost, where the salary cap stands and what needs still need to be addressed.

Who the Bills added

Matt Cassel, QB

Tyrod Taylor, QB

LeSean McCoy, RB

Jerome Felton, FB

Charles Clay, TE

Percy Harvin, WR

Richie Incognito, G

Who the Bills re-signed

Marcus Easley, WR/special teams

Jerry Hughes, DE

Jarius Wynn, DE

Who the Bills lost

C.J. Spiller, RB (signed with Saints)

Scott Chandler, TE (signed with Patriots)

Lee Smith, TE (signed with Raiders)

Erik Pears, OL (signed with 49ers)

Kiko Alonso, LB (traded to Eagles)

Keith Rivers, LB (cut and signed by Cowboys)

Da'Norris Searcy, S (signed with Titans)

How much salary cap space do the Bills have?

Right now, Spotrac.com has the Bills with just over $9.5 million in cap space. That includes the allotted money for their draft picks but does not include the contract for tight end Charles Clay. The average value of his contract is between $7 million and $8 million, but without knowing his signing bonus for 2015, his exact cap hit is still up in the air. That said, once it's factored in the Bills won't have much more room to make major moves without clearing space.

What else do the Buffalo Bills need?

1. Quarterback

No, the Bills were not able to solve their quarterback problem in free agency, and that shouldn't come as a surprise. Cassel and Taylor are nice additions for competition, but that's all they are. Credit the Bills for not forcing the issue, though. They could still add a young quarterback in the NFL Draft next month, but there's a chance Cassel, Taylor, EJ Manuel and Jeff Tuel are the team's only quarterbacks entering training camp. The goal now is to find a way to mask their flaws.

2. Offensive line

Despite adding Incognito, the Bills' offensive line is still a concern. Buffalo targeted a few offensive linemen in free agency but was unable to reel one in. Right now, the offensive line will feature Cordy Glenn at left tackle, Seantrel Henderson at right tackle, Eric Wood at center and competition for the two guard spots with Chris Williams, Kraig Urbik, Cyrus Kouandjo, Cyril Richardson and Incognito as the main candidates for the two jobs.

3. "Five-technique" defensive end

The Bills are loaded on the defensive line, particularly after bringing back Hughes, but for Ryan's scheme they could still use a defensive end that can play as a "five-technique." This player would play with his hand in the ground in a three-man defensive front and would line up on the outside shoulder of an offensive tackle. A name to watch in the NFL Draft is Mississippi State's Preston Smith.

4. Safety and linebacker depth

Whaley and Ryan seem comfortable with the starters at both linebacker and safety. Duke Williams, Jonathan Meeks and Bacarri Rambo will compete to replace Da'Norris Searcy at safety. Adding more competition wouldn't be the worst idea. Same goes for linebacker, where Nigel Bradham and Preston Brown are both quality starters, but another player behind them wouldn't hurt.

5. One more pass catcher

The idea might seem a bit crazy considering the Bills added Clay and Harvin to an offense that already features Sammy Watkins and Robert Woods on the outside. But offensive coordinator Greg Roman has been known to use two tight ends in his offense, and Clay is more of a "move" tight end. MarQueis Gray and Chris Gragg are the other tight ends left on the depth chart, and they both fit that mold as well. In San Francisco, Roman had Vernon Davis and Delanie Walker. Clay is more Walker than Davis, so the Bills may be looking for another weapon at the position in the NFL Draft.