The List
There are 570 6 letter words with U as the first letter. The highest scoring is UMFAZI at 20 points in Scrabble, though Words With Friends prefers UPGAZE at 21. 276 carry three or more vowels, which makes them useful for dumping a vowel-clogged rack.
UAKARIUBERTYUBIETYUBIQUEUBUNTUUCKERSUDDERSUGALISUGGINGUGLIEDUGLIERUGLIESUGLIFYUGLILYUGSOMEUHLANSUHURUSUJAMAAUKASESULAMASULCERSULEMASULEXESULICESULICONULIKONULITISULLAGEULLINGULMINSULNAREULOSESULOSISULSTERULTIMAULTIMOULTIONULTRASULYIESULZIESUMAMISUMBELSUMBERSUMBERYUMBLESUMBRAEUMBRALUMBRASUMBRELUMBRESUMBRILUMFAZIUMIACKUMIACSUMIAKSUMIAQSUMLAUTUMMAHSUMMINGUMPIESUMPINGUMPIREUMRAHSUMWELTUNABLEUNAGEDUNAKINUNARMSUNAWEDUNAXEDUNBAGSUNBALEUNBANSUNBAREUNBARKUNBARSUNBEARUNBEDSUNBEENUNBELTUNBENDUNBENTUNBIASUNBINDUNBITTUNBOLTUNBONEUNBOOTUNBOREUNBORNUNBREDUNBURYUNBUSYUNCAGEUNCAKEUNCAPEUNCAPSUNCARTUNCASEUNCASTUNCATEUNCHICUNCIAEUNCIALUNCINIUNCLADUNCLEDUNCLESUNCLEWUNCLIPUNCLOGUNCOCKUNCOERUNCOESUNCOILUNCOLTUNCOOLUNCOPEUNCORDUNCORKUNCOWLUNCUFFUNCURBUNCURLUNCUTEUNDAMSUNDATEUNDEADUNDEAFUNDEARUNDECKUNDERNUNDIESUNDINEUNDOCKUNDOERUNDOESUNDONEUNDRAWUNDREWUNDULYUNDYEDUNEASEUNEASYUNEATHUNEDGEUNEVENUNEYEDUNFACTUNFAIRUNFEEDUNFELTUNFINEUNFIRMUNFITSUNFIXTUNFOLDUNFONDUNFOOLUNFORMUNFREEUNFURLUNGAGSUNGAINUNGEARUNGETSUNGILDUNGILTUNGIRDUNGIRTUNGLADUNGLUEUNGODSUNGORDUNGOWNUNGUALUNGUESUNGUISUNGULAUNGUMSUNGYVEUNHAIRUNHANDUNHANGUNHASPUNHATSUNHEADUNHEALUNHELEUNHELMUNHEWNUNHIVEUNHOLYUNHOODUNHOOKUNHOOPUNHUNGUNHURTUNHUSKUNIFICUNIONSUNIPEDUNIPODUNIQUEUNISEXUNISONUNITALUNITEDUNITERUNITESUNJAMSUNJUSTUNKENDUNKENTUNKEPTUNKINDUNKINGUNKINKUNKISSUNKNITUNKNOTUNLACEUNLADEUNLAIDUNLASHUNLASTUNLAWSUNLAYSUNLEADUNLEALUNLESSUNLICHUNLIDSUNLIKEUNLIMEUNLINEUNLINKUNLIVEUNLOADUNLOCKUNLORDUNLOSTUNLOVEUNMADEUNMAKEUNMANSUNMARDUNMASKUNMEEKUNMEETUNMESHUNMEWSUNMIRYUNMIXTUNMOLDUNMOORUNMOWNUNNAILUNNESTUNOPENUNOWEDUNPACKUNPAIDUNPAYSUNPEGSUNPENSUNPENTUNPICKUNPILEUNPINSUNPLUGUNPOPEUNPRAYUNPROPUNPUREUNRAKEUNREADUNREALUNREDYUNREELUNREINUNRENTUNRESTUNRIGSUNRIPEUNRIPSUNROBEUNROLLUNROOFUNROOTUNROPEUNROVEUNRUDEUNRULEUNRULYUNSAFEUNSAIDUNSAWNUNSAYSUNSEALUNSEAMUNSEATUNSEELUNSEENUNSELFUNSELLUNSENTUNSETSUNSEWNUNSEWSUNSEXYUNSHEDUNSHIPUNSHODUNSHOEUNSHOTUNSHUTUNSNAGUNSNAPUNSOFTUNSOLDUNSOULUNSOWNUNSPARUNSPEDUNSPUNUNSTEPUNSTOPUNSTOWUNSUITUNSUNGUNSUNKUNSUREUNTACKUNTAMEUNTEAMUNTENTUNTHAWUNTIDYUNTIEDUNTIESUNTILEUNTINSUNTOLDUNTOMBUNTORNUNTRIMUNTRODUNTRUEUNTUCKUNTUNEUNTURFUNTURNUNUSEDUNVAILUNVEILUNVEXTUNWAREUNWARYUNWEALUNWELLUNWEPTUNWILLUNWINDUNWIREUNWISEUNWISHUNWISTUNWITSUNWIVEUNWONTUNWORKUNWORNUNWOVEUNWRAPUNYOKEUNZIPSUPASESUPBEARUPBEATUPBINDUPBLEWUPBLOWUPBOILUPBOREUPBOWSUPBRAYUPCASTUPCOILUPCOMEUPCURLUPDARTUPDATEUPDIVEUPDOVEUPDRAGUPDRAWUPDREWUPENDSUPFILLUPFLOWUPFOLDUPFURLUPGANGUPGAZEUPGIRDUPGIRTUPGOESUPGONEUPGREWUPGROWUPGUSHUPHANDUPHANGUPHAUDUPHEAPUPHELDUPHILDUPHILLUPHOLDUPHOVEUPHROEUPHUNGUPHURLUPJETSUPKEEPUPKNITUPLAIDUPLANDUPLAYSUPLEADUPLEANUPLEAPUPLIFTUPLINKUPLOADUPLOCKUPLOOKUPMAKEUPMOSTUPPERSUPPILEUPPINGUPPISHUPPITYUPPROPUPRATEUPREARUPRESTUPRISEUPRISTUPROARUPROLLUPROOTUPROSEUPRUNSUPRUSHUPRYSTUPSEESUPSELLUPSENDUPSENTUPSETSUPSEYSUPSHOTUPSIDEUPSIESUPSIZEUPSOARUPSOLDUPSTAYUPSTEPUPSTIRUPSWAYUPTAKEUPTAKSUPTALKUPTEARUPTICKUPTIEDUPTIESUPTILTUPTIMEUPTOOKUPTOREUPTORNUPTOSSUPTOWNUPTURNUPWAFTUPWARDUPWELLUPWENTUPWINDUPWRAPURACHIURACILURAEUSURALISURANIAURANICURANINURANYLURARESURARISURASESURATESURATICURBANEURBIASURCHINUREASEUREDIAUREDOSUREIDEUREMIAUREMICURENASURESESURESISURETERURETICURGENTURGERSURGINGURIALSURINALURINEDURINESURITESURMANSURNFULURNINGUROPODUROSESUROSISURPINGURSIDSURSINEURSONSURTEXTURTICAURUBUSURUSESUSABLEUSABLYUSAGERUSAGESUSANCEUSEFULUSHERSUSNEASUSQUESUSTIONUSUALSUSUREDUSURERUSURESUSURPSUSWARDUTASESUTERUSUTISESUTMOSTUTOPIAUTTERSUVEOUSUVULAEUVULARUVULAS