Lots of DC aliens here. A Martian (or Saturnian) Legionnaire could be cool.
In addition to the Tamaraneans, the Vegan system also has the Changralyns (Broot), Karnans (Tigorr), Warlords of Okaara, Gordanians, Emana Branx, Psions, Euphorians, Roguians, etc.
A Thanagarian priest-mystic, who uses Nth metal as a focus for his spellcasting, could be a funky twist on an old classic DC alien race.
Quite a few races, like the Dominators, like to tweak with meta-genes for their own purposes, such as the Xenobrood, Competalians, H'San Natal, Murrans, etc. resulting in there potentially being many different types of powered representatives from their worlds.
The Orinacas or Duomalians, from the 'Mirror-Verse,' could produce an interesting Legionnaire, if their champion retained some sort of mirror-verse-related powers (travel through reflective surfaces, reflect attacks, etc.).