On the lower end:
Audion Sterling KT88/EL84
Puresound A10 and A30
Consonance Cyber series
http://www.decoaudio.com/deco_audio_integrated_amps.html
Ming Da 18w SET KT90
http://www.bd-audio.co.uk/Ming-Da-MC368-B902.html
Of those I have had the Audion Sterling Plus SE KT88 and a Consonance Cyber 10SE KT88 SET and heard the Ming Da 18w SET KT90 and they are all great, the Ming Da being probably the best and the Audion close behind.
My favourite I have owned is the Decware Zen, an SV83/EL84 based SET amp with a massive 2wpc, probably not the most suitable but the best I have heard. Got a Puresound A10 coming hopefully in the next week.
Audionote Oto is one of the best I have heard as well, around £1k used and around £1.8k new IIRC. Uses EL84 tubes which I seem to prefer to the KT88/EL34 SE and PP designs
Another lovely valve power amp I have spent a day with was an original Radford STA-15, which was very nice.