Taoster about beat me to it.
Under $100
CMOY - better than most component headphone jacks, DIY only (or contract a DIYer), easily made portable or wall wart driven
$100-$250
META42 - just excellent for the price, but DIY only (or contract a DIYer), easily made portable or wall wart driven
$250-$400
Corda HA-1 (ss) - quick, tonally balanced, relatively neutral
ASL MG Head (tube) - sluggish but smooth, nice
SonicAdventure Reality (hybid) - authoritative but somewhat closed in
$400-600
HeadAmp.com Gilmore (ss) - excellent, also a preamp, but no crossfeed, new one man company
Corda HA-2 (ss) ? - crossfeed, probably worth the risk - not yet heard one myself
$600-$900
Corda Prehead (ss) - my current favorite amp, has crossfeed, also a preamp, going higher without a world class source seems pointless
AudioValve RKV II (OTL tube) - lower priced than the TwinHead, best natural soundstage out of anything I've heard, smooth, authroritative, forgiving, nice
Sugden Headmaster - smooth, fast, articulate, a little bit glossy and not quite as good bass as the others, includes remote, preamp, no crossfeed
$900+
ASL TwinHead (OTL tube) - excellent amp with great treble extension
HeadRoom Maxed Out Home (ss) - best bang for the buck HeadRoom amp, relaxed sound, more forgiving and less fatiguing than other solid states, crossfeed and brightness controls
Those are the ones I like most, anyway.