I think this is my current favorite thread…
Lead
Bead
Bend
Band
Bald
Bold
Gold
Drink–> Glass
Lead -> Gold
Lead
Load
Goad
Gold
Try…
Water -> Smoke
Drink
Drank
Crank
Clank
Clans
Class
Glass
Ok I posted water -> smoke. I’m having trouble coming up with a solution. Impossible? You tell me.
Not impossible. This is probably not the most efficient route, though:
water
wafer
safer
safes
sales
salts
malts
melts
meats
seats
spats
spits
spies
spiel
spell
shell
shall
shale
shave
shove
stove
stoke
smoke
If anyone can find a shorter route, go for it!
In the meantime, how about sword -> death
(note: untested)
Damn. I think I got it, too, only mine is much longer. Take a look at it anyway and see if it works.
water
later
lamer
lames
lares
hares
hires
sires
sores
sorts
forts
foots
moots
moote
soote
smote
smoke
(these were all checked with dictionary.com)
I’m leaving Darwin’s Finch’s as the next one. I’ll work on it some, too.
sword
swore
score
scope
scape
scare
spare
spars
sears
seats
heats
heath
death
Oops, knock out scope and scape there. Didn’t clear out the deadwood.
I can’t think of a good one right now.
Well, okay, that’s actually shorter, as any fool (except me) can see. But it uses obscure words.
I see Genseric has solved Finch’s. I’ll put in the next, since he (she?) can’t think of one.
Fool --> Dead
I haven’t tested this one, btw.
fool
foal
goal
goad
load
lead
dead
how about paper -> steel (untested, likely easy)
paper
payer
plyer
slyer
sleer
steer
steel
sane --> work (untested)
sleer?
sane
wane
wank
wonk
work
light -> heavy
http://www.dictionary.com/cgi-bin/dict.pl?term=sleer
sleer \Sle"er, n. A slayer. [Obs.] --Chaucer.
[sub]All terms used by this poster are dictionary.com approved[/sub] 
I’m gonna give someone else a shot to do one of these, though. Besides, I want to finish reading the board before I have to go to bed.
It would go something like this…
light
sight
sighs
sub[/sub]
least
lease
leave
heave
heavy
Could someone help me out?
In the meantime…
Eins -> Tein (connecting Albert Einstein’s last name reminiscent of moronmountain’s god -> fry)
Eins
Tins
tEns
tenD
Vend
venN (as in a Venn diagram)
veIn
Tein
OK, now try:
book -> tape
Book -> Tape:
book
cook
cork
core
cope
cape
tape
Next: seed -> tree
(And without resorting to foreign words, I’m not sure that light -> heavy is possible. It’s that darn g…)
Ok, this one I got…
seed
sLed
Fled
fleE
fRee
Tree
How about
sink -> swim
light -> heavy is certainly possible. I’ve solved it, but I won’t post the answer for a while, to give you guys a chance to ply your brain cells. It’s all real words, that people really use. No archaic Chaucer words, and I didn’t even use a dictionary. Just normal words. Well, one is fairly rare these days, but it’s certainly a normal usable word.
The list of words is 21 entries. Maybe you guys(and gals) can solve it shorter, too.
**sink -> swim **
sink
sins
sons
sops
bops
boas
boat
beat
beam
seam
slam
slap
slip
ship
shin
thin
twin
twig
swig
swim
Good one! Seems easy at first, but then BAM!
Light -> Heavy Anyone? Bueller?
light
Sight
sighS
siNhs
sinEs
Mines
minDs
mEnds
meAds
Heads
headY
heaVy
Sinhs is the plural of the hyperbolic sine function. I can’t find a way to do it using only normal words.