I once heard from Andrea Immer (Master Sommelier, and host of Fine Living's "Simply Wine") that every wine fan should have a wine in their home that is for once a day, once a week, once a month, once a year, and once in a lifetime. I really like this approach. As your wine collection grows (trust me, if you get into this at all, your collection WILL grow), you need ways to organize it. This is a good way to get things somewhat separated. I want to briefly give examples of the types of wines that I have for each of these occasions. Hopefully this will help you think about your next purchase a little more than simply whats on the label, or what you felt like buying that day.
Once a day-
These are also called the "everyday drinkers". This is the wine that you can sit there, eating pizza, watching CSI, and not feel bad about opening it. Depending on your financial situation, these bottles can be from $10 and under to much more (I have a doctor friend that drinks $40 and $50 bottles almost daily. I can't afford that.) I recommend buying wines like this by the case if you can, as most stores will give you a case discount. I also recommend having a case of white and a case of red, to fit most occasions. The wine that I have for this right now is the 2007 Bodegas Olivares Altos de la Hoya- a delicious Spanish monastrell that goes with just about everything. You can get it for about $10 retail. I also usually keep some bottles of Crios Torrontes (white wine option) around as well.
Once a week-
This is the wine that you will open when you are thinking a bit more about what to pair it with, and who you're drinking it with, but you still aren't going to beat yourself up over it too badly. Simply because of my wife's preferences, I usually consider a bottle of bubbly, or a decent bottle of riesling to fit the bill here. Consider bubbly from Gruet or Feuillatte, and maybe riesling from Monchhof, Von Hovel, or Dr. Thanisch. These will usually cost a bit more, maybe in the $20 to $30 range.
Once a month-
This is where you really start to see divisions in what people collect, and are willing to open. I'm a huge fan of well made California cabs, and will pop a $50 or $60 once a month. My favorite labels are Larkmead, Snowden, and Ramey. I also have friends that will bust out $200 once a month. Do what you can, but make sure it's something that you consider "nice"! After all, this is just fermented grapes that we're talking about, and they do you no good if they stay in the bottle.
Once a year-
This usually takes some planning. These are wines that typically age a little bit better, and you are probably only going to pull out on an anniversary, birthday, etc. The example that I have is a 2007 Clos de Papes Chateauneuf. This is a respectfully expensive bottle of wine (probably $120 to $150 retail), and it is nowhere near drinking age yet. I will likely keep this bottle for several years, and open it at a special occasion. It will be my "once a year" wine for that year. This year, we opened a 1995 Cos D'Estournel for our 6th anniversary, which was also the wine that we drank on our first. These are the types of wines that I'm talking about...something special, and meant for a semi-momentous occasion.
Once in a Lifetime-
These are the wines that you can't replace. I will never be able to replace the 1977 Taylor Fladgate that my friend and restaurant management mentor gave to me, that we opened when we bought our first house. Nor will I be able to replace the 1978 Richebourg that we opened when my nephew was born. Often these wines are given to you, or bought for your for a specific reason. Right now, I have a 1997 Grange that a friend of mine gave us for our wedding. He instructed us to open it on our 10th anniversary, which I'm going to do. These are the wines that make your palms sweat, your heart beat a little faster, and your hands shake when you open them, because you don't want to mess it up. They are also a lot of fun, and you had damn sure better share the occasion with a loved one, family, or friends.
So go out, buy a case of everyday drinkers, a bottle to drink this weekend, and start thinking about the monthly, yearly, and lifetime wines.