Nothing in the logs are indicative of the problem yet (including apache logs, the logs of the services being executed that utilize a lot of load, etc). I gave up looking at the logs because all of them had no problems around the time that I suspected that the server halted (other than that was their last entry before it halted and the next entry was the startup).
Hardware, seems to be good. There is only 1 primary hard drive that the operating system boots off of (was replaced earlier this year; February, I think; because the prior one was failing), then it mounts a couple of USB drives for backup purposes, and a SMBFS network share from a NAS (for both backup purposes and for reading of a few specific files).
Memory looks to be good, I usually have screen with at least one session running htop so I can quickly check vitals and memory usage. SWAP memory is always low, network is always available, doesn't run a GUI so no video to deal with, CPU and MB temps are always decent when I look (hoping munin will show otherwise the next time it occurs though!), no funny noises (so nothing sounds like it is failing or being over worked).
I'm not 100% sure SMBFS would be the culprit, because that was just a recent conversion, so the prior failure a few months ago, would have had nothing to do with that.
I do know one of the USB drives unmounts or goes unresponsive fairly regularly (I need to replace it, but just haven't had the time), so I have an automated script that runs every hour to see if it is unresponsive and if it is, to remount it. Originally, I thought that was the issue several months ago, but removing the script from cron didn't resolve the issue, it happened again within days (I believe this was a hardware issue and I replaced a few drives), but hasn't happened again until last week.
I'm just at a lost, because 1) it happens on rare occasions, and 2) none of the logs are indicative as to why it happened, if the command was harshly issued, etc.
Granted, this could have been a power surge (small enough to kill my server, and not affect any other appliances), but I have several servers located against this wall, all without UPS right now, and only this one went down... albeit, not impossible, but seems improbable to be the cause.
I might never know what exactly happened, was just looking for other indicators everyone else may consider that I may have overlooked and that I am getting plenty of suggestions on Thanks everyone for that. Hat Trick to @PromptSpace ; for the suggestion on over-heating, that got me to find munin (awesome utility!)