What is the best way to compress a video shot by my Nikon D5100 so it can be easily uploaded to Youtube? I have a video of around 600MB, I tried converting using Xilisoft video converter but without any success.
Amazingly, the best place to start with a question like this is Youtube. Believe it or not they have help file that explain the process with quite a bit of detail: https://support.google.com/youtube/bin/answer.py?hl=en&answer=1722171&topic=2888648&ctx=topic
On Youtube itself many others have offered up video tutorials on how to do it: Youtube.com search
I would take the recommendations that YouTube has on the help pages, and simply apply those settings to your favorite video software, it could be something like Adobe Premiere Elements which is a very common video editor, but many others exist.
As dpolitt mentioned, Premiere should be able to do this, but when trying for a number of videos taken at a recent conference it failed badly when trying to optimise for YouTube- it either came out with files that were far to big, or when compressed down their quality was terrible.
The solution was to run Handbrake on the output from Premiere - this comes with very simple profiles (Selecting High Profile works well for YouTube) and it runs incredibly quickly, reducing file sizes down from around 2Gb to a couple of hundred Mb per video for my 1hr videos, with no appreciable loss of quality.