Groove Tubes, TAD and EH. I have Harma power tubes, but haven't tried their pre-amp tubes.
I also have a ton of Mullard, Brimar, Tung-Sol, GE, Mazda, Bugle Boy, RCA and other original valves. I looked out a few years ago and bought a job lot of pre-amp valves for a small amount. Some of them are good, but to be honest the new ones give almost the same sound now, and are probably more reliable. The Groove Tube 12AX7M is a great preamp tube.