Having recently moved to Linux only on my laptop, the one tool I was having trouble replacing was Winmerge, the recommended visual diff/merge app for Tortoise users and popular SourceForge project. On the advice of Andrew, I checked out Meld – a similar Linux tool. Wow, no looking back.
The one hitch I had was installing from src – usually this is not a problem but in this case I ran into quite a deep dependency tree of Gnome libs. However, the RPM from Fedora Core 2 works fine on Core 3 – give it try.