You'll definitely know diacetyl when you taste it in excess. It's a distinct cloying butterscotch flavour that makes a beer hard to drink. I can't give an example because when it reaches the level where you'd pick it out, it's a major flaw! It can be a background note in some styles and helps to round out the flavour, but generally if it jumps out at you, the beer shouldn't be on sale.
Esters usually have very distinctive fruit flavours and aromas (many are used as flavourings in food). There's an ester that smells like apples, one for raspberries, pineapple, etc. so when people say they're fruity, that really is the best description. A specific ester would very rarely if ever appear on its own in a beer so you may struggle to pick them out individually. Esters can come from fermentation by-products or hop oils, but generally when homebrewers talk about an "estery" beer, they're on about the yeasty ones. These are generally most apparent in lightly hopped beers fermented with English ale strains.
Phenols are pronounced in Belgian beers more than any others.. Think cloves, spices, medicinal notes etc. Belgians also show strong ester characteristics as well.
It's very hard to give commercial examples that would be similar but for the esters... They would be totally different beers even if the base recipe was similar, and that's almost impossible to pick out. I reckon your best bet might be to brew a very simple recipe with just a small amount of bittering hops, then split it into 4 fermenters and chuck 4 different yeasts at it. WLP001 - Very clean, hardly any esters, WLP002 - Very estery English strain, WLP500 - Classic Belgian flavours, estery and phenolic, WLP300 - German hefeweizen, strong banana ester and clovey phenolics.
Edit: just remembered.... If you don't want to brew it yourself, Brewdog actually did something very similar called "unleash the yeast". They used an Pilsner yeast in place of the English one and their base recipe is quite hoppy, but the idea is the same:
http://www.masterofmalt.com/beer/brewdo ... east-beer/
Get yourself a box of that and see if you can pick out the flavours!
Also, if you have a Brewdog bar nearby, they do something called "beer school" where they crack open some interesting boozes and talk you through the flavours. I've never done one so I can't speak for the quality, but it might be worth a go.
