A product whose demand is price elastic is one that is easily avoided if the price is too high. Products in this category would be considered luxury items, as opposed to necessities.
In hard times, few people are willing to spend a significant amount of money for entertainment and amusement. So I would pick Movie Admissions and Sporting Events as products whose demand is price elastic.
Substitutes for these products would be DVD rentals (for Movie Admission Tickets) and watching sports events on TV (in lieu of actual game attendance)
Complements would be Pop Corn sales at the movies, and Beer and Hot Dog purchases at actual sporting events.
One of the most elastic good in our society is oil. The price of oil changes dramatically. For instance, the barrel of oil can jump to 150 dollars a barrel and go down as low as 80.00 dollars. This will have an impact on the price of gas, travel, and pretty much all goods. Some substitutes in the future hopefully will be electric cars, solar energy and the like. The less oil we use, the better it will be for all people.
Premium channels on cable TV would be another example. We have chosen a very basic range of cable channels. It would be nice to have more, but we don't watch TV enough to justify the extra expense. Most of the films we might watch can be rented cheaply from Netflix, and many of the "exclusive" shows (such as The Tudors) eventually become available on DVD.
One product that is highly price elastic is gourmet coffees: as prices rise, customers drop off; with lower prices, popularity and customers soar. Substitutes are old fashioned coffee, tea, and herbal teas. Complements are sugars and sugar substitutes, creams and creamers, Danishes and donuts (!), and--in some cases--books.
Outside of what has been answered, all great suggestions/examples, I would have to say clothing. As the parent of a teenage girl, I have been diligently trying to explain to my daughter about jeans and labels. So, for the question, let us say that the jeans from "Hollister" would be elastic. Jeans from "Aeropostale" would be a good substitute or a department store (not according to my daughter though) would be the substitutes.
Bicycles would be another good illustration. Bikes can be stripped down to one gear and fat tires that work acceptably on flat paved roads or sidewalks; bikes can sport multiple gears on exotic alloy frames with clip-in pedals, aerodynamic handlebars, ergonomic saddles, and computerized accessories to monitor heart rate and calories burned by the rider in addition to distance and speed at which the bike is moving. The attire of the biker is a whole different set of complementing items.
Another good could be running shoes. There are incredibly expensive high end models with all sorts of gadgets and fancy bits and there are also cheaper and simpler alternatives going down the price scale to very inexpensive and likely poorly made knock-offs of brand name shoes. Complements include of course various kinds of socks up to the newly popular tall compression socks or other running accessories.
Cell phones would be a great example too. There are high-end Iphones and other smart phones, but if cost is a factor, a more simple messaging phone or simple call only phone would be serviceable. Within the area of phones, there are also substitute and complementary phone service plans.
I was thinking along media lines, but with new computers. Substitutes would include older models of those computers or cheaper brands. Complements include the variety of broadband and wifi services on offer and all the other things you can purchase to go with them.
A likely good that would be price elastic would be big screen TVs. Substitutes for these include smaller screen TVs, computers with large monitors and good graphics programs, and movies. Complements might include cable TV subscriptions, satellite TV subscriptions, high definition DVRs, video games like Kinect, and services like Netflix.