One of the big agile players is now affordable for the little guy. VersionOne has released V1: Agile Community which is a free 5-user version of V1: Agile Enterprise. It has all the same functionality with only the user limit. There is a disclaimer that is doesn't include support, training and upgrades. Upgrades? I hope they keep this product up to date.
Watch out when you hit user #6. That will force an upgrade to Enterprise which is $995 for the original five and $500 / user after.
V1: Community Edition