A relatively small quantity of alcohol can make a big difference in a dish, whether added in the form of wine or a spirit such as brandy. Brandy's concentrated flavors lend intensity to meat sauces and aroma to cream sauces, and it's widely used in recipes from the European canon. If you don't have brandy on hand, or don't want to use alcohol in the dish, don't panic. Lots of alternatives exist, both alcoholic and non-alcoholic.
If you're keen to keep the flavor of your recipe as close to the original as possible, brandy extract is an obvious choice. It's commonly used in dessert recipes to replace brandy's aromatic and slightly sweet notes, but it's just as applicable to savory dishes. Dilute 1 part extract with 4 parts water, and incorporate it into a sauce or marinade as you would with the brandy. Skip over any steps that call for igniting the brandy, because they're not necessary. Some extracts are alcohol-based, but once they're diluted, the alcohol is unobtrusive.
Raising Your Spirits
If you have no objection to using alcohol in your dish, but simply don't keep brandy on hand, other aromatic spirits can be useful substitutes. Vodka is flavorless and of little use, but many other varieties of liquor can bring an interesting spin to your recipe. Bourbon is earthy and slightly sweet, and Scotch adds an intriguingly smoky note. Gin's crisp, woodsy herbal note isn't suitable for all recipes, but it works very well with game and game birds. All of these options -- and less obvious ones, such as rum or tequila -- change the flavor of the final dish, so use them judiciously.
Wine About It
At bottom, brandy is simply wine that's been distilled to give it deep, concentrated flavors. When you have no brandy on hand, you can achieve a reasonably similar result by adding a strong wine instead. Dry sherry, Marsala, tawny Port, and similarly rich-flavored wines are all good options, providing similar depth and subtlety. Some varieties are sweeter than others, so you might find it necessary to add a splash of vinegar or lemon juice to balance the flavors. Ordinary wine will also work, especially if you boil it down to syrupy thickness before it goes into your recipe. Use a full-bodied white wine, rather than red, if you want to maintain the original color of your dish.
Any brandy brings a hint of residual fruitiness to a dish, and some -- especially fruit-based brandies such as France's famed Calvados -- bring a great deal. A simple splash of fruit juice can be a useful alternative to the brandy in many dishes, yielding a flavor much like the original. Apple juice or white grape juice are good general-purpose replacements for brandy in many recipes, especially those involving pork or poultry. If your recipe originally called for a fruit brandy, use the corresponding fruit juice, and then add a few drops of vodka or other reasonably neutral spirit, if you wish, to complete the resemblance.