[NANOG] Introducing latency for testing?

So I want to mimic some latency in a test network for DB replication. I am wondering what other's have used for this? Obviously, the best way to would be to actually have one box across the US or across the globe to actually test against but what if you don't have that? Are there any GPL software router solutions that would allow you to tweak the latency in between the two test boxes? Thanks in advance. -Mike