Contact-based soldering irons fall into two primary categories. Resistance heating and RF heating. The low-price, low quality irons use an element that gets hot when current is passed through it (think light bulb, or nichrome wire). You can find some good stations with thermistor or thermocouple-based temperature control for around $70-$200. Weller makes a good line of relatively inexpensive irons that will get you a long way, if you have some basic soldering skills.
The next level up are the professional-grade irons. Many of these use high-frequency radio waves to heat the tip of the iron. Many of them operate around 9-11 MHz (some industrial sized bulk heaters also run in this frequency range). Those solder stations are quite expensive, as are the iron tips. We use them at my work, but our lab techs have them in-hand 7 out of 8 hours a day, in a lot of cases.
I'd recommend a good Weller iron with a variety of tip sizes for different types of soldering jobs... 1 small, 1 medium, 1 large. The more metal you have, the better you can heat and remove large solder joints. The smaller tips won't dump as much heat into your target, but are handy for dealing with small pins on ICs (i.e. memory chips, as you mentioned).