There are a few bottlings from the Veneto that are amazingly consistent and always offer great value. I'm thinking of La Palazzola and La Grola from Allegrini (who makes divine Amarone that can even be called a value at $60 or so) and Zenato Valpolicella Ripassa (which is a Valpolicella that is allowed to macerate with the spent pits/skins used to make Amarone).
Skalogre's recommendation of Taurino's entry level bottling, Salice Salentino, is a good one, but for just a little more you can have their Notarpanaro, which is several steps above the base wine in quality. It's a great example of (good) traditional southern Italian wine - aged in barrel/tank for several years before release, which is more and more a rarity in Italy (although plenty of Spanish producers still do this).
Moving north, I really like some Dolcettos, particularly from the Dogliani region. Luigi Einaudi comes to mind, but there's a lot of producers there that specialize in the varietal. It's really incredible how dark a wine Dolcetto can produce, considering its reputation for lightness (a term which is usually used perjoratively when applied to the Dolcetto).
There's a zillion Cotes du Rhones that will fit the bill, but for $20 you should be able to get a decent Gigondas or Vacqueyras that will offer more interest. One of my all-time favorite sub-$20 reds is Domaine du Cayron's Gigondas - certainly meaty and sauvage
, but also sweet and approachable.
With the past string of very ripe vintages in Bordeaux (starting with 2003), the quality of wine produced by the lesser chateaux has jumped, so there's a variety of bargains there. Maybe check out a well-reputed Fronsac like Fontenil, which IIRC is one of Michel Rolland's original properties.
In California, I'd zero in on Zinfandel for value red wine. Rosenblum comes to mind (although only a fraction of their bottlings are sub-$20 now), as does Edmeades. A lot of Zins from Amador are also relatively inexpensive.
I could go on...so many countries...Spain, South Africa, Chile, Argentina, Australia...
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