One of the many things I learned at linux.conf.au was about ack. Thanks to Paul Fenwick for bringing it to our attention. Spend a few minutes with me on this...
If you are a fan of grep (especially with -drecurse), but hate seeing the .svn directories and contents of the object files, you need ack.
Colourised outputs, highlighting, nice organisation, awesome configurability are all bonuses. Even has documentation.
Packages exist for at least Debian and Fedora. Portable (perl), installable using CPAN.