rwmichel

What are the triangular shaped bags called that sit in the corner of your horizontal bar and seat tube?

Are there any recommendations

BarracksSi

No recommendations from me, but you'll find them called "frame bags".

I've actually got two that I bought from a shop when they were liquidating inventory, but even though one fits at the front and the other at the rear, I can't fit both of them at the same time on my 58cm steel bike.

This was one of the first Google hits:
https://www.bikebagshop.com/bike-frame-bags-e-329.html

10 Wheels

Nashbar has one on sale:

https://www.nashbar.com/bikes/Product...7_10000_200352