Practice Squad:

As of August 19, 2014, practice squad sizes increased from 8 to 10 players for the 2014 and 2015 seasons. In addition, eligibility was modified in two ways: 1) a player officially accrues a “season on a practice squad” after having spent 6 games on a squad in a year. Previously, this threshold was 3 games. 2) Each team may carry up to two players with no more than two accrued seasons towards NFL free agency. Apart from these two players, a player who has accrued one or more seasons towards NFL free agency is only eligible for a practice squad if he has spent fewer than 9 games on the 46-man active roster in his accrued seasons.

Note: I have included waived/injured players on this list as they may become practice squad candidates once healthy.

Eligible for the 2015 10 man practice squad

All drafted and undrafted rookies
Matt Barkley
Matthew Tucker
GJ Kinne
Quron Pratt
Freddie Martino
Josh Reese
Josh Andrews
Jared Wheeler
Kevin Graf
Taylor Hart
Frank Mays
Wade Keliikipi
Jeremy Towns
Brandon Hepburn
Travis Long [IR]
Deontae Skinner
Marc Anthony
Jaylen Watkins
Jerome Couplin
Ed Reynolds
Brandan Bishop

Eligible for the two 2-year veteran practice squad spots

Excludes those who are highly unlikely to be cut, such as Lane Johnson or Jordan Matthews.  Note that those denoted by a * become ineligible for the practice squad after their their 6th game on an NFL roster in 2015.

Kenjon Barner
Trey  Burton
Josh Huff
Jeff Maehl*
David Molk*
Matthew Tobin*
Brandon Bair*
Beau Allen
Marcus Smith

Not eligible for the PS in 2015

All players on this list are not eligible because they have dressed for too many NFL regular season games in a prior season and have accrued more than 2 years towards free agency.

Tim Tebow
Riley Cooper
Julian Vandervelde
John Moffitt
Brayan Braman
Emmanuel Acho
Chris Prosinski

[Updated 08-27-2015]

The official 2011-2020 CBA (Article 33) language on who is eligible for the practice squad:

The Practice Squad shall consist of the following players, provided that they have not served more than two previous seasons on a Practice Squad: (i) players who do not have an Accrued Season of NFL experience; and (ii) free agent players who were on the Active List for fewer than nine regular season games during their only Ac-crued Season(s). An otherwise eligible player may be a Practice Squad player for a third season only if the Club by which he is employed that season has at least 53 players on its Active/Inactive List during the entire period of his employment.
See also the August 2014 addendum press release.

The NFL and the NFL Players Association have agreed to expand NFL Practice Squads for the 2014 and 2015 seasons. Absent an extension of the agreement, the current rules will be reinstated beginning with the 2016 season.

Under the agreement, 2014 and 2015 Practice Squads will increase from the current maximum of eight players to 10 players.

In addition, the criteria for Practice Squad eligibility has been expanded in two respects.

First, a player must have a minimum of six games – up from the current three games – on a Practice Squad in order for that season to count as one of the player’s three permissible seasons of Practice Squad service.

Second, each club will be permitted to sign a maximum of two Practice Squad players who have earned no more than two accrued seasons of free agency credit. Absent this exception, a player who has earned one or more accrued seasons would not be eligible for a Practice Squad unless the player spent fewer than nine games on a club’s 46-player active list in each of his accrued seasons.

All other practice squad rules under Article 33 of the 2011 Collective Bargaining Agreement will remain in effect during the 2014 and 2015 seasons.