Words that work as html colors:

accede beaded bedded beefed decade deeded deface facade

Words with seven consecutive consonants (counting y):

encrypts
nonsynchronous
rhythms
strychnine
unsynchronized

Words with five consecutive consonants (not counting y):

angstrom
birthplace
corkscrew
downstream
hardscrabble
jockstrap
latchstring
lengthly
(wave)lengths
lengthwise
nightclub
offspring
postscript
postscripts
sportswriter
sportswriting
strengths
switchblade
witchcraft
worthwhile(ness)

Knightsbridge has six, but it's a proper noun.

Words with five consecutive vowels:

queueing

Words of seven or more letters that can be typed on the right hand of a qwerty keyboard:

billion
bobolink
bullion
hillbilly
million
minimum
monopoly
opinion
pumpkin

Words of eight letters or more that are typed only on the top row:

etiquette
perpetuity
potpourri
prettier
priority
property
proprietor
propriety
prototype
puppeteer
purporter
repertoire
repertory
reporter
territory
torturer
typewriter

Five letters or more only on the middle row:

alfalfa
falls
flags
flash
flask
galls
glass
halls
salad
salads
shall
slash

Long words whose letters alternate between the right and left hands (there a lot more coming as soon as I'm bored enough):

antisocial
proficient

Words whose letters alternate between consonants and vowels, counting y (all of which start with a vowel):

aboriginal
aborigines
analogical
analytical
anatomical
anemometer
apologetic
apologized
apologizes
economical
economized
economizer
economizes
ejaculated
ejaculates
elaborated
elaborates
eliminated
eliminates
eliminator
elucidated
elucidates
enumerated
enumerates
enumerator
epitomized
epitomizes
eradicated
eradicates
evaporated
executives
italicized
operatives
originated
originates
originator
uneconomic
uneconomical

The best rot13 pairs:

terra, green
vex, irk
sync, flap
nowhere, abjurer
tang, gnat
ones, barf
onyx, balk
try, gel ("There is no gel -- only solid and liquid." -- Lbqn)