My site is built around a busy plugin (Feed WordPress), so turning it off isn't really an option. DreamHost won't tell me how much memory I'm using or how much I'm allotted so I don't really have enough information to understand the problem. I think this TPC memory plugin will help, Thanks! I've heard of people having memory issues with VPSs as well, so before I move to another hosting company or a VPS, I want to have a good idea of how much memory I'm using.
Here are the links the DreamHost people sent me about memory issues.
DreamHost: All right it looks like you're hitting our process watcher. This exists to make sure no one exceeds the memory limits on your shared server which would cause problems for all the other users on the server. When your script(s) consume too much memory, it will kill the process. The end result is an entry in your error.log and a 500 error on your page. We have a few wiki articles that may help you find the source of this and troubleshoot it further:
http://wiki.dreamhost.com/index.php/Finding_Causes_of_Heavy_Usage
http://wiki.dreamhost.com/User_resource_reporting
http://wiki.dreamhost.com/index.php/Bots_spiders_and_crawlers
DreamHost: Since you're also using WordPress for this site, definitely check out the wiki pages below as well as they contain information specific to optimizing WordPress:
http://wiki.dreamhost.com/WordPress_Optimization
http://wiki.dreamhost.com/Fine_Tuning_Your_WordPress_Install