You can look up past cap values here:
http://asp.usatoday.com/sports/football/nfl/salaries/default.aspx
You can look up all base salaries here
note that these amounts change often becuase of escalators, some incentives and performance bonuses are added to the base salary so when the player earns them their base salary info will change without notice or warning. Also keep in mind that their search only shows 25 players at any given time so it is best to search by team and position or last name so you dont keep any names off the 25 player list they show)
http://www.nflpa.org/Resources/ActivePlayerSearch.aspx
As for signing bonuses, other bonuses, incentives, escalators, and any other misc. stuff you will just have to hope that the media reports that info and you can find it on the net. Most media will just say 20 Million gauranteed without breaking it down by signing bonus, roster bonus, option bonus, or any other bonus. And they rarely tell you about incentives or escalators and will just give you what the total contract could be.
Or you can just wait until Feb before FA starts and I post my yearly Cap spreadsheet. Like I have done the last 2-3 years.