For main caps, rod caps, and cylinder heads, recommended bolt torque values are readily available.  But what about the rest of the engine?  Like water pumps, headers, or covers?

And what about the rest of the car?  Transmission crossmembers, subframes, engine mounts, shifters, and so on.  Usually I just do as tight as I can depending on how squished I am because I was too lazy to jack the car up.

Is there a guideline for bolt torque?  

The best torque reference that I have found for smaller bolts is ARP.  

However, I would definitely check and see if the manufacturer gives their recommended torque specifications for area of the part you need it for.   Because the torque you may need to apply may not be limited to the bolt, but limited to the holding power of the threads in the body.  

With that said...

Check out:  http://www.arp-bolts.com/catalog/Catalog.PP/2005Catalog024.html

Good Luck.