Here's Heisman on the 2,000 tactical patterns. But yeah, the 5,000 rings a bell but I thought it was a study on grandmasters. 
8+ tactics books which together may contain 97% of the ~2,000 basic tactics patterns (*= good three to start):
- Chess Tactics for Students - John Bain* (can do repetitively - see above)
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Bobby Fischer Teaches Chess - Bobby Fischer and Margulies*
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Starting out: Chess Tactics and Checkmates - Chris Ward*
- Winning Chess Strategy for Kids - Jeff Coakley (a great author)
- The Chess Tactics Workbook - Al Woolum
- Back to Basic: Tactics - Dan Heisman (use cleaned-up 2nd printing)
- The Winning Way - Bruce Pandolfini (more difficult to find)
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Power Chess for Kids - Hertan - a helpful book about how to find basic forcing moves, easier than Hertan's also very good Forcing Chess Moves; check out his helpful essay "Adventure and Sportsmanship" on p.13, but his key exception on p.19 has exceptions itself!
Need more basic patterns? Throw in:
Checkmate for Children by Kevin Stark has an excellent array of basic checkmate patterns
The Art of the Checkmate by Renaud and Kahn
Winning Chess Traps - Irving Chernev
Winning Chess Tactics - Seirawan & Silman - not a great problem set, but good explanations of the Tactics - in that sense similar to Learn Chess Tactics by Nunn
Novice Nook on why using these puzzles to reject your candidate moves is the main idea for studying basic tactics
Novice Nook on 
I once read something along the lines of Class C players knowing 5000 positions on average and it further went on to explain how man positions a expert typically knows then a master etc... I know this isnt much to go off of but anyone know what im talking about ?