It looks like a couple weeks ago I was hit with a Google algorithm change (my guess), and all my pages - that ranked on the first two SERPs - suddenly now reside on 4-5, or not at all. Obviously this kind of thing hits a lot of us from time to time, but this one puzzles me.
When I search for something like our products, I get pages that have fewer to none of the keywords I searched, and even fewer backlinks. In other words, some pretty poor pages beat mine. They are not very relevant. My pages are keyword rich for sure.
I still have a page rank of 4 (which dropped from a 5 a few months ago). I don't know if I'm being penalized for something.
I guess I don't really know what my next move should be, except to go through and keep trying to optimize for the words that my keyword research suggests. And to keep building backlinks. Your thoughts are appreciated!!!

I definitely wouldn't start panicking yet FTR. I noticed some unusual movement in Google for a couple of my "on the cusp"* sites over the past couple of weeks also. Whatever they're doing it seems like they've been waffling back and forth a bit. Where I'm seeing a particular phrase that is may normally be Page 1 for me (5-10 ranking) suddenly jump back to Page 2 or 3. Then another time I check it'll be back up there in the Top 10 again.
If you're going to do anything at all I would suggest trying to putting some effort into getting some more good quality, targeted inbound links. Not only will these help stabalize things in the short term, but in my experience they'll also help to limit such bouncing around in the future once you have a solid, diverse set of links pointing towards your site.