I've noticed that plenty of colleges and conservatories do not have a specified Etude for auditions. Do any of you know some good ones that will impress them?

With a quick Google search for "flute etude audition", I found this:

http://www.depts.ttu.edu/music/SOM/Downloads/Bands/Auditions/ConcertBand2009/FluteFall09.pdf

There are other similar results that you can look at.

The Karg-Elert seem pretty popular for college auditions (and I have had several students who went to college and worked on them in their first year). Anderson etudes are good. I like the Karg-Elert more because some of them have more of a melody. With Anderson I feel like I am just moving my fingers a bunch.

Kohler Etude Op.33 - book 1 (beautiful melodies)
Kohler Etude Op.33 - book 2 (melodies + impressive)
Kohler Etude Op.33 - book 3 (very impressive)

I agree on many of these suggestions, many of the Andersen etudes have gorgeous melodies, but they are hidden amongst all the notes

many of the Boehm etudes are very nice too