Try >>4979 and >>4983 for starters; I also use Leechblock as backup.
Breaking your work up into smaller chunks works great, I'll do work for 30-45 mins then read a book for 10-15 and come back to my work refreshed.
For long-term results, read more books and spend less time on the internet. Heavy internet users have more white matter in their brains and have similar brain activity to drug addicts when they browse; I find that after spending several days reading more and browsing the internet/Jewtube less, my brain feels clearer and less fuzzy. It helps me focus on tasks that need doing.