On MirBSD and other sane OSes, you can just press ^T (Ctrl-T) when dd(1) runs; this sends it a SIGINFO (cf. sigaction(2)) which asks it to display (progress) information to the tty. This includes kFreeBSD, btw.

Update 07.01.2012 — this also works on Hurd. Linux neither has SIGINFO nor (cooked mode tty) support for it.

There’s also pv:

	dd if=/dev/mapper/vg01-${customername}--hudson bs=1048576 | \
	    pv -pter -B 1048576 -s 85899345920 | \
	    xz -0 >/mnt/ci-${customername}-snap-20120105-lenny.img.xz

I used this At wOrk today to back up a Jenkins VM before upgrading its underlying operating system for evaluation. Here, the -s flag is the total size (in bytes; don’t forget to multiply by 1024 when reading from Linux’ /proc/partitions) so pv can calculate a total and an ETA; -B is the same as bs; and xz is the currently best compressor to use, in any situation, unless you must stay compatible to gzip(1)-only systems. (Except that it’s not under an Open Source licence.)

clpbar might also be worth looking into. XTaran points out sid has this as bar.

PSA: Last of June, 2012, will be a leap second.