.. also about CentOS/RHEL, CentOS team recently released a 6.0
Minimal CD ISO image (290MB) which includes rather cut CentOS 6.0 system, but after installation we end up with about 590MB of used space and what we got? Alomost nothing, it even does not include
wget (but
curl is there), there is no compiler, no ncurses, no ... nothing actually. At least LVM is available.
Compare that to minimal FreeBSD install which includes (with
base/manpages/kernel datasets) complete C/C++ compiler also BIND, sendmail and and FTP server, latest ZFS v28 and DTrace and all that on 230MB[*].
OpenBSD and NetBSD probably would take even less space.
[*] Modifications:
# rm -r /boot/kernel/*.symbols
# cd /boot/kernel && gzip -9 kernel