Escort Specific Sites:     
FEOA-Ford Escort Owner's Association: One of the most informative escort site on the web. Talk to fellow escort owners on the message board, get tuning tips, info about available parts for escorts, and much more.  Recently remodeled and better than ever.
Escort Racing Developement Team: The other top escort site.  For the most active forum around, go here. Unfortunately ERDT is current gone.  At this point it's not known if it will be revived.
ZX2.com: Not really for my car, but they have tons of info for any zx2 owners out there.
ZX2 Racing: Affiliate of zx2.com, they have even more info and a great message board.
ZX Tuner: The store of ZX2 and ZX2 Racing.  Lots of escort parts!  Support out community and buy from them!

 

Misc. companies that make stuff for escorts:     
Weapon-R: The only company I know of that makes an intake for the 1.9L escort.  Also some other cool stuff too.  -Coilovers now available for 91-96 escorts!
Corksport: Many parts for 2nd gen scorts, lots of good hard to find parts.
Gude: Aftermarket camshafts, heads kits, and more.
Grant Steering Wheels and Accessories: They have tons of different steering wheels and a nice euro kit wheel adapter for 91-96 escorts (#6532).
B & M: I have their Pro Edge Short Shifter (#45097) in my scort.  Excellent quality from the name known for shifters.
Eibach: They make some nice lowering springs for escorts. (Pro Kit- 1" drop)
Ground Control: Of course everyone knows about the awesome coilovers that ground control makes.  Raise it, slam it, whatever.
Erubuni Aerodynamics: One of the biggest producers of body kits, and they make one of the few available for the 2nd gen escort.
Rod Millen Motorsports: They sell some parts for gt's, and also the cool aero grill and top spoiler for 2nd gen scorts.
SuperChips: Plug this chip into your ECU and get a claimed 9-13hp and 12-15ft lbs!  These are proven to work too, maybe not as well as claimed but still.
CTA motorsports: The first company to make an intake for the 3rd gen SPI, and they have a 2nd gen intake coming soon.
Perfekt Performance & Composites: aka PPC Racing; They have some suspension and brake kits for escorts.
Pacesetter: They make headers for most cars, mandrel bent cat-back systems, and a short shifter for 91-up escorts. 
Black Diamond Racing: They make a underdrive pulley for 1.9l and 2.0l SPI engines.
Andy's Autosport: They now produce body kits for both 91-96 and 97-up Escorts!
FX Designs: Canadian company that will soon debut a body kit for 91-96 Escorts.
OnderGround Designs: Another maker of a body kit for 91-96 Escorts.

 

Ford Escort groups on Yahoo!
1st gen and EXP group
Escort GT group
Escort Racing Developement group
General Ford Escort Group

 

Misc Parts:    
Southwest Ford Racing Performance Parts: Some good prices on Ford Racing parts for the ZX2.  Note all the suspension parts will fit all 2nd gen, 3rd gen, and ZX2s.   Specifically look at the ZX2 tokico struts for only $160.  Best deal around!
Magnaflow Exhaust: Check out the straight through design mufflers.  I have one of the mirror finish stainless mufflers on my 1.9l, and it sounds nice and smooth.  No raspy, tinny honda sound with one of these bad boys.
Dynomax Exhaust: I personally don't have any experience with dynomax's, but they are well known and been around for quite a while.  Check em out.
Hose Techniques: Get a cool hose kit and give your car some color under the hood.  High quality silicone hoses available in many colors; in seperate lengths or full kits.
Venom Performance: Computer modules, fuel pumps, injectors, and now nitrous kits.
Energy suspension: Polyurethane bushings for almost any suspension application.
Progress Technology: More suspension stuff, they make springs for escorts and they make lots of other stuff too.

 

Online Stores:     
Directpart: These guys have almost all the parts (new AND used) that you'll ever need for ANY car.
Carparts.com: Everything you need for any car.  Flat out.
J.C. Whitney: Lots of accessories for any and every car.   Now featuring a sport compact section.
Cyber Auto: Another site with literally tons of parts.   They can get you basically any part for your escort, and most other cars too.
Jeg's: Maybe you can find something you need here.   Mostly parts for your big ass V8, but there is a sport compact section.
Summit Racing: Kinda like jeg's, but of course it's a different company.
Red Pepper Racing: Online raceshop up in canada.   Remember the exchange rates!
Ptuning: Another online import raceshop.  This is the only place I've found that sells Progress Technology Springs for the escorts. Easy to find stuff here too-  just pick escort and then your year on the side and it'll tell ya all the stuff they have.
Tire Rack: Tons of wheels and tires.  And in the wheel section it'll show you the wheels on an actual picture of an escort.  Just make sure you pick '94 and up cuz there's no picture when you pick 91-93.
Tires n Parts: Another site with tons of wheels and tires.   They sell stuff on ebay really cheap sometimes too.
Nopi: These guys are well known.  Lots and lots of stuff.
Xtreme Flow: Very low priced, high-flow catalytic converters.  They also sell mufflers too.
oVerboost store: Good prices on a HUGE selection of parts.