That question can't really be answered. I'll give you a list I like, someone else will give you a list he or she likes, and you'll end up with a random assortment that won't do you much more good than simply going into a store and buying randomly.

If you want to understand the grape, you could do a lot worse than buying the Washington wines - Columbia Crest and it's big brother, Chateau St Michelle. The former is about $8 and the latter $14 or so, but worth the difference in price IMO. And there are a number from up there that are perfect examples of decent, drinkable, merlot - Canoe Ridge, Cougar Crest, etc.

Chile makes some inexpensive ones but the only one I would drink is Casa Lapostole Cuvee Alexander - it's about $18 or so. Moving up in price, Whitehall Lane Reserve is plummy and delicious really, as is Stelzner's and any number of others. You can pay $50 or so for Pride. Most great cab producers produce a decent merlot.

And then you can buy Petrus from Bordeaux, which is about $1600 or so.

What you might try is to buy the merlot and the cabernet sauvingon of some of the above producers. Taste side by side and you'll see the difference in the grapes. Then take differing amounts of one blended with the other. That's what winemakers do. They often soften the cab with a bit of merlot, or toughen up the merlot with a bit of cab. See what combo you like. And remember that in the US, you can call something merlot or syrah or whatever, but it need not be 100%.

And then move beyond merlot.

Cheers.