I am basically in love with this. I regularly get told that my startup disk is nearly full on my MacBook Pro, and always turn to Grand Perspective to see what I can clean up (yesterday it was a whopping 19 gig of cached files from the Twitter app). Not the newest or prettiest of apps, but definitely one of my favourites.

I use this tool all the time, it's a huge help

This is a lifesaver for freeing up space during upgrades

Been using Disk Inventory X (http://www.derlien.com/) for years. Gets the work done.

I still prefer DaisyDisk (http://www.daisydiskapp.com/) for this, but Grand Perspective is pretty neat!

Does everything you need it todo though. Gives you a representation of where your data is being stored. + you can "reveal in finder" to be able to manually delete files taking up space on ur hdd.

Pros:

Free

Cons:

Not a great UX