Possible Swaps
Now before someone jumps on me and says anything is possible with enough time and money, I know. These are going to be fairly straightforward options with the pros/cons.
D series swaps
These are fairly inexpensive and come in a variety of Civics. IMHO, these are the easiest swaps to drop in. I also don't want to hear a bunch of whining about the opinions on power levels. Of course there are going to be some exceptions to the rule.
Pros
Inexpensive
Decent potential (200 whp or so on stock internals)
OEM parts are cheap
More than enough for most people
The best D series come with ~130 hp tops
Optional factory LSD in the JDM D15B
Cons
Not as much potential as some other motors
Transmission not geared for accelleration
Don't respond to bolt ons well
Only way to get real power out of them is FI
B16
These can be found in the JDM SIR and SIRII (among other JDM cars, which I don't claim to know all of which it came in) as well as the USDM 99-00 SI (EM1) and the 99-00 Canadian SIR.
Pros
160 hp stock
High RPM power
Fairly inexpensive
Good transmission
DOHC VTEC
Cons
113ft/lbs torque (very little more than a D16z6 stock)
Without knowing what you're looking for you can end up with a high mileage JDM model
Under 4k or so it feels just like a D16
B18B
This is the motor in the non Type-R and non GSR Integra.
Pros
Good torque for a 1.8L (127 ft/lbs)
Inexpensive (even cheaper than a B16)
142 hp (more than any stock D series)
Boost heads love them
Cons
No VTEC
Longest B series transmission
B18C1 (or JDM B18C)
These come out of an Integra GSR.
Pros
Good Hp and TQ numbers (170, 121 ft/lbs respectively)
DOHC VTEC
Tons of potential
High revving
Cons
Expensive
Becoming moreso as people keep scooping them up
Slighty longer tranny than the ITR and B16
B18C5 (or JDM B18C)
This is found in the Integra Type-R. IMHO this is the best swap for a Civic.
Pros
GREAT HP and TQ numbers (195 and 134 ft/lbs)
High revving
Hand built motor from Honda
Optional factory LSD
Best transmission for a B series from the factory
Red valve cover
Cons
EXPENSIVE
If JDM ITR is used, the 36mm axle 32mm hub problems occur
B16B
This is the motor found in the Civic Type R found all over the world.
Pros
185 hp 117 ft/lbs
High revving
Good top end power
Red valve cover
Cons
Expensive- almost as much as an ITR for lower performance
Very little torque still, have to rev the motor to make power
B20
Pros
Great torque (133 ft/lbs)
good boost motors
inexpensive
B20z=146hp
Cons
Thin cylinder walls
Have to peice together a swap for a Civic (can't drop it in with a B20 tranny)
Won't pass BAR (light truck motor in a car)
Low hp in the B20b(126 hp)
H22/JDM F20B
Pros
200 hp
H22=156 ft/lbs torque
F20B=145 ft/lbs torque
Great torque
DONT WEIGH THAT MUCH MORE THAN A B SWAP!!
http://honda-tech.com/zerothread?id=684550
Cons
Harder to install than a B/D motor
transmission feel is vague IMHO
Less info out there for the swap (aka, less experience as they are less common)
Price of swap is comperable to a B18C5 after everything is said and done (mounts, etc)
K20
This can be found in the new EP3, the RSX (base and Type S) as well as other cars across the world (RSX R, etc). This is the future of the swap IMHO. There is a writeup on installing one of these in one issue of Sport Compact Car magazine (June 2004 I *think*)
Pros
200 hp 158 ft/lbs torque (RSX R)
I-VTEC
Respond VERY well to bolt ons
6 speed transmission
Most have very low miles
Cons
Still super expensive
More difficult swap than a B or D