Tobias has darkrai and Latias. I also remember another guy from the battle frontier having an articuno which fought Ash's Charizard. Are there more trainers with Legendary Pokemon in the anime?
Well firstly, the person you seem to be referring to with the Articuno is Noland. The Articuno he uses against Ash was befriended by him and wasn't technically captured and hence, not his pokemon.
Since you specified Anime, I will stick to mentioning trainers only from the Anime who have Legendary Pokemon. At the same time, I think it is fair to disregard Evil Teams who managed to control Legendary pokemon/ Trainers who have befriended Legendary Pokemon and even used them in battle.
The following trainers in the Anime have Legendary Pokemon
- Brandon: He is the Frontier Brain of the Battle Pyramid and considered to be the strongest Frontier Brain in the Battle Frontier. He owns a Regirock, Regice and Registeel.
- Tobias: He is the Winner of the Lilly of the Valley Conference(Sinnoh League). He owns a Darkrai and Latios.
- Random Trainer in the Lilly of the Valley Conference(Sinnoh League): In Episode 182 in the anime, we see a random trainer registering a Heatran for the Pokemon League. However, we never see this trainer or Heatran in any of the matches in the tournament apart from this episode.
- Nurse Joy part of the Gym inspection Agency: In a Diamond & Pearl Special, we see Nurse Joy use a Latias against Brock's brother Forrest.
- Gladion: He is Lillies Brother and Ash's reccuring Rival in the Sun & Moon anime. He has a Type: Null which later evolves into a Sylvally.