All right, so roughly speaking, here's what's the what at our key needs:
Backup QB: Ryan Fitzpatrick has signed, but there are other mid-range options who could beat him/Hamdan out in camp if the Bills are so interested. Only Collins has signed, so there's Frerotte, Trent Green, Brad Johnson, or Byron Leftwich if you want experience.
Emergency RB: Fred Taylor was a real interest, so the Bills are looking. Rumored to be interested in Kevin Jones, also look for Deuce McAllister, Ahman Green, or LaMont Jordan accepting a backup job.
#2WR: There's still Coles! And Housh, though that's a longshot. Marvin Harrison is an option for a year, maybe, and depthwise, you could make a (weak) case that Jerry Porter or Nate Washington is better than Josh Reed.
TE: Chris Baker was the only real option.
OG: No need to panic here: Mike Goff, Kendall Simmons (visited already), Geoff Hangartener, and Pete Kendall would all fill gaps.
C: Matt Birk or bust, now. Though some of the guards, (Hangartener!) can play center.
DE: Almost nothing happened here today, so the options are wide open - Chris Canty, Antonio Smith, Kalimba Edwards, Igor Olshansky
DT: Rocky Bernard would be a solid pickup, and I like Jovan Haye. And like every other year, there's always Grady Jackson.
OLB: Wide open - Freddie Keiho, Cato June, Derrick Brooks all have extensive T2 experience. Then there's Keith Brooking and Michael Boley
S: Jermaine Phillips, Sean Jones, and Mike Brown headline here.
So, the moral here is that if you have a need at every position, there will be players available for you.