The technical stuff: What makes sparkling wine sparkling is a secondary fermentation. For the first fermentation, the steps are exactly the same as those for making still wine - sugar (from the grapes) + yeast (indigenous on the skin of the grapes or added by the winemaker) = fermentation and alcohol. This still wine is then held in a pressurized environment while more sugar and yeast are added. This second fermentation under pressure results in CO2, and, thus, bubbles when you open the bottle. Couldn't be easier.
The conditions of the secondary fermentation are a large part of the method that determines how the wine will taste in the end. There are two primary methods of secondary fermentation: The first, or the traditional method (called methode Champenois in Champagne), is the one developed in Champagne that gives the wine its unique characteristics. Long story short, many of the flavor characteristics common to Champagne and other traditional method wines (toasty, brioche-y, biscuity, nutty, etc., flavors) are due to the way in which the secondary fermentation takes place - a long, laborious process that involves prolonged contact of the wine with the spent yeast cells (called lees) in the bottle in which it is sold. Note that Champagne must be made by this method, as must Cava, Cremants, and Franciacorta. This is generally regarded as the most high-quality way to produce sparkling wine (although there are persuasive arguments to the contrary).
The other main way of producing sparkling wine is the charmat, or tank, method. In this style of production, the still wine is put into a pressurized tank, into which the dosage is added and the secondary fermentation takes place. The sparkling wine is then funneled under pressure to the bottle. The result is a sparkling wine that lacks the above mentioned bready, etc. flavors and is instead a clearer expression of the grape within (which can be somewhat obscured by the traditional method - explaining why the relatively aromatically neutral Chardonnay grape is so often favored in these wines), which is why it's fantastic for two of my favorite summertime sparklers.
The first is the gorgeous Moscato d'Asti, produced in the Piedmont region of Italy. Now, in my mind, this is a very stylized wine. It's super-aromatic, showing off the floral, peachy and honeyed aromas that are hallmarks of its Muscat grape. It's also sweet, as a result of its production method which is a twist on the tank method. But I can't imagine a better wine to accompany ripe berries and cream, or just on its own as a light dessert. A bonus is its low alcohol (usually about 5-7%, as opposed to the 12-12.5% in other sparkling wines), which can help it be a great finish (or start) to a meal that doesn't go straight to your head. One person I know terms it "fun juice," and he's not far off. Try pretty much any brand in your wine store. Just don't confuse it with Asti Spumante, which is Italian for "dreck."
The second, light, aromatic, super-summery wine that I love is the one that belongs in my kir royales (or mimosas, or bellinis, or ... well you get the drift) is Prosecco. This wine is produced all over Northern Italy and is named for the grape and is normally described as aromatic and crisp. The wine is vivacious, with bright lemon and lime aromas and is perfect for the hottest summer days, since it doesn't have the richness with which traditional method wines are generally associated. This also makes it great for combining with the fruity mixers of brunch cocktails. An overwhelmingly popular brand is Carpene Malvoti - which also happens to be quite good. Just drink it as young as possible.
Finally, a sparkling wine story that puts all of this into some perspective: I was at an evaluative tasting last year for various sparkling wines. The coordinator saved for last Andre (couldn't help myself, - try this link instead), expecting that all of our educated palates would crush this inferior, inexpensive wine. But, to everyone's surprise, the wine wasn't bad. It wasn't a subtle, refined Champagne, to be sure, but we didn't spit it out in disgust either. Lesson learned - it really is just fermented grape juice.
