When Adam Kaplan first released Devel::NYTProf, I loved it. It stole the code grid feel from Devel::Cover, and it worked well.
Now, Mr. DBI, Tim Bunce, has done some amazing work and released Devel::NYTProf 2.0. Follow the link and check out the screenshots.
As cool as everything looks, and as helpful as the color-coding is, the big advance in 2.0 is the clickability:
On lines that define a subroutine NYTProf now adds ‘comments’ giving the total number of times the sub was called, the inclusive time spent in that sub, and the average. Then it adds a break-down of the same details for every location that called the subroutine.
For anyone concerned with finding bottlenecks in Perl code, Devel::NYTProf is clearly the gold standard.
Version 2.04 now produces profile data files about 1/10th the size of the previous versions. I've a blog post about it. That page also has a link to the screencast of the talk I gave at OSCON 2008 about NYTProf.