Nothing is strictly better than Ack, but some tools beat Ack in specific ways.

• The Silver Searcher (or Ag for short)

  A mostly-compatible clone of Ack. Written in C, mostly by Geoff Greer. It uses tricks like pthreads, memory-mapped IO, Boyer-Moore-Horspool strstr(), and PCRE's JIT to improve performance. It also supports some extra features, such as obeying gitignore/hgignore/svn:ignore. Geoff has written many posts about improving Ag.

• AckMate

  A TextMate plugin for Ack. There is also a fork that runs Ag.

• ack.vim

  A vim plugin for Ack. You can use Ag with this plugin as well. Just open your .vimrc and add let g:ackprg = 'ag --nogroup --nocolor --column'.

• Exuberant Ctags

  This program builds an index of functions and variables. Searching is extremely fast, but limited to what's in the index. Good for very large codebases.

• git-grep

  Fast. Built into git.