1. Classic Black Blazer: A very good jacket can do a lot for your overall look. You could wear just a T-shirt and jeans, but an expensive, fabulous jacket upgrades your outfit. Can be used in casual settings or for dress or work situations as well.
2. Jeans: Here is one many people are puzzled about. There are so many cheap jeans out there now that they think, "why should I spend $200 when I can get a perfectly cute pair for $50?" The answer is: fit. The fit is truly better when you spend more on a quality pair. Also, jeans are worn literally hundreds of times, probably more than anything else in your closet so spending more makes sense. You want them to last through many washes and wears. Splurge on one or two pairs of premium denim in a dark wash. If you can, it's also great to hem one for flats and one for heels.
3. LBD: Every woman needs a beautiful, well fitting black dress that can take you from meetings to dinners, and everything in between. Choose a beautiful, classic style that won't go out of style in one or two seasons and if you need to, have it tailored to fit you perfectly. And don't go too short, that can kill it's longevity. Right above or at the knee is best.
4. Coat: It must really fit, and the fabric must be of a caliber that will withstand heavy wear and won't wrinkle. Go for a classic style here as well, either single or double breasted in a wool or wool blend. The more wool, the more expensive. However, wool blend coats with too much polyester tend to look cheap. A more expensive coat will simply hang better.
5. Suit: If you are a person that needs suits for work and the like, then spend here as well. It's a definite wardrobe "building block" and should be of high quality, light weight "seasonless" wool usually in black or a dark color.
6. Slacks: A classic, lightweight wool slack is also essential to every woman's wardrobe and the more expensive (fully lined) are usually going to fit better and be more flattering.
7. Shoes: Now here is one that is not straight forward! I believe you should spend on some shoes, but not all. A classic black pump that goes with everything, a beautiful leather boot that will last for years, those kinds of shoes should definitely be the ones to splurge on. However, any of the more trendy items (wedge sneakers, anyone?) should be something you save on. The trend will not be around long and you will be glad you didn't break the bank when you are putting them in that Salvation Army pile!
8. Cashmere sweaters and silk blouses: (If you want to).... this one is not written in stone. I think a beautiful cashmere sweater, in either a turtleneck or v-neck, is something that looks beautiful and is timeless. However, I would say only spend on these if you can afford it and you want to. There are many less expensive sweaters now, or try to get something at and end of season sale. It's not that these go out of style, but I find mine get pilled (yes, even the expensive ones!) or eaten by moths before I would have actually stopped wearing them. As for blouses, just try to have a couple that are really silk as the polyester never looks as good or as classy.
Now I'm sure you are saying, "Well, where can I save?" To that I say, anything trendy (those wedge sneakers again! and overalls!) or that you think is so "in" that it will definitely be "out" sooner rather than later. Also, some shoes (as noted above). These could be trendier ones or shoes you just wear out or in the evenings. These don't need to be as comfortable as a work shoe or something you wear everyday and therefore, you could save on these. While on the subject of evenings, all evening wear can also be a "save"as you will never wear it the amount that justifies spending more. Two other places I think you can be cheap, t-shirts and gym clothes. No one needs $100 yoga pants! There are pretty high quality gym clothes that are relatively inexpensive (you are just sweating in it after all!) around these days. And t-shirts, don't get me started on the $100 t-shirt! GAP, Old Navy, J Crew all have good quality 100% cotton t-shirts for under $50.
Now go shopping!!