Can I convert an image from CMYK to RGB in Mac OS X?

I found three ways to do it.

1. Open the image with ColorSync.
2. Use the Apply ColorSync Profile to Images action in Automator.
3. Use sips (thanks NSD) and supply the --matchTo argument. I wrote a shell script to convert an image using the Generic RGB Profile.

#!/bin/sh

if [ $# -lt 1 ]; then
    cat >&2 <<EOF
usage:
    $0 filename
    $0 source-file destination-file

    Converts an image to RGB color space. The first form manipulates
    the file in-place.
EOF
    exit 1
fi           

SOURCE_FILE=$1

if [ $# -lt 2 ]; then
    DESTINATION_FILE=$SOURCE_FILE
else
    DESTINATION_FILE=$2
fi

sips \
    --matchTo '/System/Library/ColorSync/Profiles/Generic RGB Profile.icc' \
    "$SOURCE_FILE" \
    --out "$DESTINATION_FILE"

On my machine (10.6.2), two RGB profiles are offered: "Adobe RGC (1998)" and "Generic RGB Profile". Gimp (free) can do the conversion, too.

I didn't have the RGB colorsync profiles, so I imported the files into iPhoto and then exported them again. The exported photos were in RGB. Voila