Physical memory usage issues with WordPress plugins

Actually, there is a way to tell which plugins may be the problem. The P3 plugin (ironically, written by GoDaddy) can be used to generate a report of what each plugin is doing in terms of runtime. Longer run times will usually correlate with more resources consumed and give you some initial guidance on which plugins to examine first.

Edit 2020:

So the P3 Profiler plugin might be dead. There is a new Health Check plugin from Automattic that should do an adequate job of replacing P3 and if you have shell access to your server/site, you can also use the WordPress Command Line Interface (wp cli) and run wp doctor check --all for more complete checks.

Now a days Godaddy allows us to buy a higher physical Resource Level. Buy 1024 and use less plugins, I had same issue with my site but I used fewer plugins and bought 1024 (Resource Level 2). Now my site is running well with 10k visitors daily.