TubeNet

I use Rochut for lyrical and Tyrell etudes for technical, as recommended by my teacher.

The Voxman is more or less the industry standard, and while it's a little tougher than the Rochut stuff, your student will probably enjoy the challenge. It includes lots of Blazhevich which is good for us tuba players who are familiar with those etudes (without the pesky trombone clef issues in the actual Blazhevich trombone book).

Also, take a look at some of the new Steven Mead books: New Concert Studies and a book of Allen Vizzuti etudes. Both have accompanying CD's with Steven playing to give a good concept of sound. The musical interpretations are decidedly tame so the student can use it as a point-of-departure.

Good stuff,
Mike Forbes

I picked up euphonium as an adult and Legato Etudes for Trombone based on the Vocalises of Giuseppe Concone by John Shoemaker were really helpful for me.