Despite internet folklore, shaking the carboy does a decent job at aerating. Sometimes even more than than using a pump.
It's all about surface area. According to JZ, it's not really important to pump the O2 into the actual beer, as little is absorbed when it's released, it's absorbed when its in the headspace and in contact with the beer. He also said that draining the kettle into the carboy isn't that effective at aerating.
So it's important to get the o2 into the carboy, and then shaking it does a good job of allowing a lot of the wort to get surface area contact with the air in the carboy. So, a pump without o2, doesn't really do any better than shaking it.
According to wyeast, spashing and shaking the carboy for 40 seconds is as good as a pump for 5 minutes.
http://www.wyeastlab.com/hb_oxygenation.cfm
I was about to get a pump, but I'm saving for true o2 system (probably the williams brewing one). In the meantime, I just shake the hell out of it until I get tired.