The 10gen folks behind MongoDB don't provide a prebuilt image of MongoDB and its binaries for FreeBSD, so we build our own. We then put up the tarball somewhere that our Jenkins build/test system can find it.
We only need the binaries under bin/, e.g.:
$ tar ztf mongodb-freebsd7-x86_64-1.8.1.tgz mongodb-freebsd7-x86_64-1.8.1/ mongodb-freebsd7-x86_64-1.8.1/bin/ mongodb-freebsd7-x86_64-1.8.1/bin/mongofiles mongodb-freebsd7-x86_64-1.8.1/bin/mongod mongodb-freebsd7-x86_64-1.8.1/bin/mongodump mongodb-freebsd7-x86_64-1.8.1/bin/mongorestore mongodb-freebsd7-x86_64-1.8.1/bin/mongos mongodb-freebsd7-x86_64-1.8.1/bin/mongo mongodb-freebsd7-x86_64-1.8.1/bin/mongostat mongodb-freebsd7-x86_64-1.8.1/bin/mongosniff mongodb-freebsd7-x86_64-1.8.1/bin/mongoexport mongodb-freebsd7-x86_64-1.8.1/bin/bsondump mongodb-freebsd7-x86_64-1.8.1/bin/mongoimport
FreeBSD ports maintainers keep pretty current so we build from there:
cd /usr/ports/databases/mongodb sudo make sudo make installmkdir -p /tmp/mongodb-freebsd8_64_1.8.2/bin cp /usr/local/bin/mongo* /usr/local/bin/bsondump /tmp/mongodb-freebsd8_64_1.8.2/bin/tar cf /usr/local/www/apache22/data/koansys.com/static/mongodb-freebsd8-x86_64-1.8.2.tgz mongodb-freebsd8_64_1.8.2
Now you should be able to use it in your own buildouts.
Here's the MongoDB-1.8.2 I just built for FreeBSD-8 64bit.