Miss WinDiff? Try WinMerge!
Just downloaded it - wow! It is head-and-shoulders above WinDiff. Very easy to open 2 files at once (WinDiff made it hard to know if you had opened one or two - no feedback on the process). Help docs succinct, lots more options - and it's free!
Ironically, I just found that I did have WinDiff on my system. More options!