Every time I read up on fossil monotremes, they all turn out to be either closely related to platypuses (platypusses? Platypi?) or Echidnas.
So in the vein of my previous attempts to make sense of the fossil record as I see it, I wonder, are any fossil monotremes known that AREN'T immediately recognisable as a Platypus or Echidna? Or has the group Monotremata pretty much always been just 'Platypuses and Echidnas'?

(I realise that fossil monotremes are extremely rare and fragmentary but you'd think they'd find something besides another giant platypus or echidna)

You're right: there are few monotreme fossils to go around. What we do know was summarised in a paper published earlier this year on _Teinolophus_, an Early Cretaceous Australian monotreme now thought to be a basal platypus. Early Cretaceous _Steropodon_ and Miocene _Obdurodon_ are also platypuses, as - probably - is _Monotrematum_ from the Palaeocene of Argentina. Besides that, we know of fossil echidnas, but they all belong to the extant genera _Zaglossus_ and _Tachyglossus_. That's it! Given evidence indicating that echidnas and platypuses are sister-taxa, there should be echidnas going all the way back to the Early Cretaceous.

A number of Mesozoic taxa (namely _Ausktribosphenos_, _Bishops_, _Ambondro_ and _Asfaltomylos_) have been identified as close relatives of monotremes, forming with them a clade dubbed Australosphenida. If monotremes are part of this group, they presumably diverged during the Lower Cretaceous, as their supposed closest relatives [_Ausktribosphenos_ and _Bishops_] are this age. However, some workers fail to find support for inclusion of monotremes within the australosphenidans, instead putting monotremes pretty much on their own as sister-group to Theria. If this is right, then there should be stem-monotremes going back to the Triassic, which is when monotremes and therians diverged. Where are all the Triassic and Jurassic stem-monotremes, if this is correct? No-one has reported any yet.