Really depends on what you like, and how how much you want to spend. I think between $10 and $20 per bottle is kind of the sweet spot in terms of quality and price.
On the budget side, there are a lot of good inexpensive Argentinian reds. Grapes like Malbec and Temperanillo. You can often find a decent Malbec for under $10.
If you like big heavy duty flavors, go for a Cabernet Sauvignon. If you prefer lighter body, try a Pinot Noir.
I used to work for a wine distributor, and one of our biggest sellers was McManis Family Vinyards, from CA. They do quite a few red varietals, and they are all very drinkable and fairly inexpensive. They even make a good red blend box wine under the name Jack Tone. I actually like boxed wine because it keeps for a while after you open it. A couple other decent boxes are Bota or Black Box. Just stay away from the boxes like Franzia or Vella.
On the higher end of the price scale, I really like Spanish reds, from regions like Priorat, Jumilla and Rioja.