
It seems like no matter what you blog about - no matter how innocuous - somewhere out there is a community dedicated to doing the exact opposite, in as vocal and destructive a manner possible. Angry mobs, basically, who may eventually choose your blog as a target.
Start by performing triage: first, stop the bleeding. Turn off commenting on your blog to stop the main avenue of attack. DO NOT DELETE THE ANGRY COMMENTS. You want to preserve them as evidence. If there is a way to unpublish them so that they cannot be seen but are still accessible through your admin panel, excellent. Otherwise, just let them stand.
If you have a community of readers, you may want to post a bland notice that "Commenting has been temporarily disabled." No matter what, do not react to the comments, either publicly or privately!
Next, act defensively: make a backup of your blog. This will protect you in case the bad guys are able to knock your blog offline, hack the database and destroy it, or convince your hosting company to turn off your account. (I have seen all of these things happen, and more.)
How you back up your blog will depend on your software and hosting company. You may be able to export your posts into a flat file, or you may need to log into a MySQL control panel separately and create a database backup directly.
If you don't know how to back up your blog, go figure it out today! A) everyone should back up their blog regularly, and B) don't wait until the heat of the moment to try and figure it out.
Now that you are safe, take a deep breath. Go outside or do some chores, anything to take a break and get some perspective. These attacks were not your fault. There is no point trying to engage the angry mob; you won't change their opinions, and it will only make you angry.
Keep a copy of all communications, particularly death threats. There's not much point reporting it to the police, but you never know when you will need evidence.
Remember that this is a form of bullying - meaning that it's not your fault. You may have voiced an unpopular opinion, talked trash about a celebrity or TV show that has a vocal fandom, or just committed the (to some) unpardonable sin of "being female on the internet." Regardless, you have the right to say whatever you want on your blog without being attacked.
If you batten down the hatches and refuse to engage (i.e. play dead), they will soon move on to their next target. It's hard to do, but you have to sit on your hands and let it pass.