If you have Rules, Token, and Entity API enabled, you could be exhausting your memory due to issues with Entity Token.
It's set to 128M
I have experimented from 32M to 512M in 8M increments restarting after
each attempt but the php out of memory error does not change except for
the amount it tries to allocate which I had down to 6k at one stage with
memory_limit set to 512M.
Roger
> what is your max memory limit set to in php.ini? Sometimes it's set to
> 64M out of the box.
> http://drupal.org/node/207036
>
> -Don-
>