Radial Engineering PowerTube by kyzer
Excellent sound for the price, this little pre has some bite!
Radial's customer service is also great. I stripped the hardware in my unit trying to replace the tube and they fixed it up for me no hassle.
Dial the right balance between TRIM and GAIN to get the sound you're looking for, and you're good to go, but there's more!
Make sure to give the unit time to warm up.
Air and HPF switches
Omni Functionality with Radial Racks (Hi-Z Input)
60db of Tube Gain, can really make things crunchy
Fixed Air and HPFs
Not too much clean gain/trim