Norn's Annex has only big-time siblings: Moat, Propaganda, Ghostly Prison. However, it is accessible with colorless mana, making it a unique entry in the group, and it protects your planeswalkers to boot.
This has had casual demand ramping the price gradually for a couple years now, but a price spike seems imminent.
Get FOILs under $1.50 each, or go with FOILs at or under $3.00 each. Foils will likely be pushing $10 by this time next year. Foil reprints are quite unlikely.