I was getting OutOfMemoryErrors when running Eclipse with multiple projects open. To solve the problem I added the following arguments to my quicklaunch:

eclipse -vmargs -Xms512m -Xmx1024m -Xss2m -XX:MaxPermSize=256m

Reference

-Xms

Specify the initial size, in bytes, of the memory allocation pool. This value must be a multiple of 1024 greater than 1MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is chosen at runtime based on system configuration.

-Xmx

Specify the maximum size, in bytes, of the memory allocation pool. This value must a multiple of 1024 greater than 2MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is chosen at runtime based on system configuration.

-Xss

Set thread stack size.

-XX:MaxPermSize

Specifies the the maximum size for the permanent generation heap, a heap that holds objects such as classes and methods.