How about the 7th level cleric spell/9th level magic-user spell, Gate?
One of the 2e spells that I DID like was Conjure Phoenix (or Summon Phoenix, whatever it was called), which was a 6th level druid spell (or priest spell), if I remember correctly. Barring that, maybe we can summon phoenixes with Gate instead
Of course, Gate is a very free spell, so it may be hard to specify rules for what to summon exactly (demons? planetars? gods?), and whether it will be helpful, neutral, or hostile...
Also, note that the druid ability to summon other types of elementals at high levels is not really explained very well in Unearthed Arcana - there are two possibilities, I guess:
1. The abilities can be used to modify a casting of either Conjure Fire Elemental or Conjure Earth Elemental (note that their ability to conjure fire or earth elementals is not listed) into a Water Elemental, Air Elemental, Paraelemental, and so on. Trying to conjure any type of elemental/paraelemental rolls on the tables given for druids in Unearthed Arcana, + or - the level of the druid (they can try to choose what they want to summon).
2. Druids are granted equivalent spells of Conjure Water Elemental, Conjure Air Elemental, Conjure Ice Para-elemental, and so on. (This was sort of the method chosen by later 2e incarnations, although not exactly in this case.) We do have to choose whether the spells are 6th level or 7th level, though.