Compound miter saw. Some people like sliding compounds, others laser-guided, but my dual-bevel Delta 10-inch has served me well for 18 years, especially with crown molding. The Delta 36-085 10-inch dual bevel, about $200. Alternative: Miter box and saw, metal or wood, probably $40 total.
Nailer. Black & Decker's FS1802BNB Firestorm 18-Volt 18-gauge cordless brad nailer ($135) is the hands-down choice. Unjamming it is a snap; rarely fails to perform.
Table saw. Look for versatility at a reasonable price. Delta is most enduring; mine's 21 years old and is still tops. The Delta 36-977, 10-inch, left-tilt 11/2 horsepower, about $350. If buying used, check rip-fence accuracy. Alternative: circular saw. I prefer cordless, but you need to keep batteries - even higher-voltage - fully charged for reliable cutting. Dewalt DC300K 36-volt cordless Nano 71/4-inch runs about $95.
Drill/driver. Basically for pilot-hole drilling because you don't want to split the wood with screws. The Ryobi - 18-volt with lithium ion battery - is the one (two, actually) that I use. About 300 drywall screws to a battery change. $85, but there are deals.
Level. Most versatile is the Stanley 43-512 9-inch lighted magnetic high-impact torpedo level, about $12. The light is a must for 60-year-old eyes.
(All available at local home centers and hardware stores, or at amazon.com)