I want some Veronica with very tall spikes. It looks like all of the ones sold around here have been crossed to make them short. Which cultivars have the best spikes?

How about Pseudolysimachion kiusianum ex. ‘Maximum’ aka
Lapis Tiger's Tail (Veronica ovata subsp. kiusiana)

I think it is currently considered a Veronica, properly, but you may want to google the old name, too, for more info.
https://www.anniesannuals.com/...

Cool! It's amazing that these plants are being ruined by making them short and squatty. They need to be tall!

Veronica Charlotte may be a good choice

Jennifer - Thanks! That is exactly what I wanted! I had no idea there was one with white around the leaves and white flowers! I think that will work perfectly for my white garden I'm working on.

It is the white plant in the center of my avatar

That is a pretty variety, Jennifer!

Also, they often spray PGRs on the potted plants for sale so some might actually grow larger the next year. You may have to make a list of the taller cultivars and check tags even on some that don't look tall enough in the pot.