CAGR based on daily data

Perhaps =(VLOOKUP(L4,$B$3:$C$45,2,FALSE) / VLOOKUP(L3,$B$3:$C$45,2,FALSE) ) ^ (1 / (MATCH(L4, $B$3:$B$45, 0) - MATCH(L3, $B$3:$B$45, 0) + 1)) - 1

You have a lot of redundant calculations in there. An alternative:

      -----L------ --M--- ---------------------------------------N---------------------------------------
  2   CALCULATIONS Helper Formulas                                                                       
  3   7/26/2010        13 M3: =MATCH(L3, $B$3:$B$45, 0)                                                  
  4   8/26/2010        36 M4: =MATCH(L4, $B$3:$B$45, 0)                                                  
  5                                                                                                      
  6         10.69%        L6: =INDEX($C$3:$C$45, M4) / INDEX($C$3:$C$45, M3) - 1                         
  7          -6.95                                                                                       
  8          0.42%        L8: =(INDEX(C$3:$C$45, M4) / INDEX($C$3:$C$45, M3) ) ^ (1 / (M4 - M3 + 1) ) - 1

That's what this does:

=... ^ (1 / (MATCH(L4, $B$3:$B$45, 0) - MATCH(L3, $B$3:$B$45, 0) + 1)) - 1

... and this:

... ^ (1 / (M4 - M3 + 1) ) - 1