Grainger - Lincolnshire Posy (2 independent Euphonium parts in Fennell version, lots of solos)

Grainger - Molly on the Shore
Grainger - Colonial Song
Grantham - J’ai été au bal
Holst - 2nd Suite in F (famous for its solos)
Margolis - Terpsichore (multiple solos and soli, plus a 5-part Tuba/Euphonium ensemble in Mv.4)

Sullivan - Pineapple Poll (Dunno if this is really about featuring Euphs so much as the Euphoniums are in rare form doubling all the crazy woodwind technique that permeates this piece)

Vaughan-Williams - Toccata Marziale

Schuman - When Jesus Wept (Beautiful Euphonium solo feature)

Marches:
Grainger - Children's March
King - Melody Shop (big Euph feature)
Sousa - Fairest of the Fair
Chambers - Boys of the Old Brigade
King - Invictus (doubles the crazy Flute/Clarinet lines along with T-sax)