What's your "diminishing returns" preamp choice?

What preamp would you consider is at the point of diminishing returns for you? I realize this is a vague and subjective question, but I think it will be interesting to hear the answers.

Of course, a $10,000 preamp will (probably) sound better than a $1,000 preamp but everyone has a different point at which they feel they have spent enough money. In some cases, one may feel that there isn't a significant difference between a $2k piece and a $10k piece to justify such a purchase.

I've noticed that there are some gems in the audio world that defy their price point. For instance, Apogee Centaurs, Halfer 9505 etc. I've always found such pieces fascinating.