Choosing Codes or sequences with excellent Auto-Correlation properties
There is a vast literature on this subject. In particular, deleting one bit
(the leading bit in one specific implementation) from each of the Walsh-Hadamard sequences and applying a permutation to the remaining $2^n-1$ bits will result
in $2^n$ sequences of length $2^n-1$ that consist of

(i) the all-zeroes sequence

(ii) the $2^n-1$ cyclic shifts of a pseudonoise (PN), or maximal-length linear  feedback shift register (LFSR), sequence

A PN sequence has ideal autocorrelation properties, but the cross-correlation
between a sequence and its cyclic shift has a peak value that is the same as
the autocorrelation peak.

For more than you probably want to know, I refer you to the paper
D.V. Sarwate and M.B. Pursley, "Cross-correlation properties of pseudorandom and related sequences," Proc. IEEE, vol.68, pp.593-619, May 1980.  It includes a
detailed discussion of the Gold sequences mentioned by JasonR as well as the
small sets and large sets of Kasami sequences that you will encounter in some
applications.