Here we can add useful links.
I find this page very useful for beginners:
http://www.digitaldialects.com/Croatian.htm
Great topic, and here is my contribution (these links are intended mostly to the advanced users):
Probably the best spelling checker: http://hacheck.tel.fer.hr/
Croatian sleng: http://www.zargonaut.com/
Language tips #1: http://savjetnik.ihjj.hr/index.php#
Language tips #2: http://stitch.blog.hr/
Croatian Special Field Terminology: http://struna.ihjj.hr/en/ (still beta)
Sretno s učenjem hrvatskog ;) If you have any questions, feel free to ask!
http://basic-croatian.blogspot.com.au/2009/01/1-basic-features.html
These 96 lessons are extremely detailed and useful to the beginner (ie. me).
http://www.fsi-language-courses.org/Content.php?page=Serbo-Croatian
Even though it says "Serbo-Croatian", it still gives you a choice between Serbian and Croatian. Also, it is very good for explaining grammar.
http://eurotalk.com/nl/resources/learn/croatian
first useful words and phrases for a holiday in Croatia.
[Dutch <-> Croatian] with pictures
What about the pronunciation? Does it sound as it should?
Awesome resources everyone, thanks for all of these links!