There are actually three sizes of nailers for molding---depending on the size and type of molding. 15 gauge, 16 gauge, and 18 gauge. Large crown molding sometimes requires 15 gauge finish nails, while door trim actually is done with small staples in the door jamb and 15 or 16 gauge nails into the framing.

Thye one nailer that can do both jobs is a 2&1/2" finish nailer in 16 gauge.

Google the words cordless nailer to see if there are any cordless models. There are cordless framing nailers, but I have never looked for any cordless finish nailers. Cordless are run with a power source(butane/etc) and a battery(for ignition) and do require regular cleaning and more maintenance than oiled models.

There are compressor/nailer deals available(Amazon for on line and Homd Depot/Lowes/etc for in store deals. Most of the ndeals include two or three nalers and the compressor for under $300.

In addition to what HandyMac says (and I concur), there are portable CO2 packs that eliminate need for a compressor. For regular operation, you will pay for the convenience and portability, but it's another option for the small job user.

See the below link and watch the movie. Lowe's has exactly the same thing (but painted blue and labeled Kobalt).

The most common cordless nailer that I know of is Paslode. I saw a couple of trimmers last fall using these exclusively. I kept wondering why they would use this instead of a 50' hose? Seemed a lot slower to me.

another option

Here is a link that might be useful: Jac-Pac

I love my Paslode angled finish nailer. Bought refurbished on ebay for