I have a 1997 4-door Neon with a manual tranny and 2.0 16 valve SOHC engine that is rather weak. Can anyone tell me which DOHC engines will bolt up without major modifications? I would even like to consider a turbo if it is doable without major $$$$. The car body and tranny are in excellent condition, so it would be worth a little modification. Thanks for any suggestions!

cheapest way to turbo you car would be find a wrecked srt 4 and swap motor and turbo even that way will not be that cheap.
a dohc motor will drop right in without any real modifacation you need wiring harness the computer and the motor for the dohc. and it will all drop right in and bolt up

You can put a N/A 2.4l from a minivan, 4-door Stratus or PT Cruizer. You would need to get the intake and exhaust manifolds from a 2.0 dohc and 24lb injectors. The 2.4l runs a little sluggish with the stock 2.0 sohc controller (the 2.4l needs a few more degrees of ignition timing), so you will want to get a MP or AF/X controller. You may also need a DOHC hood with the "power blister" on it to clear the Dohc cam gears. There are a few little mods and tweaks you will need to do, but so many people have done this swap, there are several places you can get step by step instructions.
You can expect about 170hp at 5800 rpm and 165ft lbs torque at 4600rpm without the Turbo. If you need more power, you can add it later after you get the 2.4l running the way you want.

2.4 Swap How-to (http://neon-owners.org/neon/tech/howto_files/24DOHC_conversion.html)
DOHC Swap (http://forums.neons.org/viewtopic.php?t=80202)

Enjoy!