Do you have any recommendations for something simple?
It depends on what your specific needs are with respect to persistence and other aspects of your application. Take a look at http://blogs.digitar.com/jjww/2009/01/rabbits-and-warrens/ and read about RabbitMQ and ZeroMQ to see if either sounds like a solution for your problem.
Lock contention will be a bitch past a certain number of processes/threads accessing the DB. Also, hopefully your application doesn't crash during the long-running work. If so, your messages are gone forever.
As for a simpler idea, message queues aren't that difficult. Why not just install a proper one to start off with.