In the past I've always used Animation Shop Pro (comes Paint Shop Pro) for creating animated gif's... not aware of any free tools but I'm sure theres something out there... link:
http://www.corel.com/servlet/Satelli...=1047024390003
... it costs $39 but I know that it would work
also alot of expensive video editing packages have output to .gif ... if you were editing the video with something like Premiere or Final Cut
[edit]dug this up... may be worth a shot:
http://www.evanolds.com/movtogifsimple.html
[edit 2]the free one that I just posted works... here's a sample gif from some random video that I found on my computer:
but it looks like you may have to resize your source video first to use this tool