How do you guys debug large programs?

[Gary Willoughby]

This is quite an open ended question but i wondered how you guys 
debug your D programs (i'm talking about stepping through code, 
setting breakpoints, etc). The lack of nice IDE's with integrated 
debuggers is worrying when working with D but up until now i 
haven't need one.

Now i've started to write much larger programs, i'm wondering 
which debuggers do you use? Especially using Linux.