Most Atari games that I want are new ones produced by the AtariAge company in Texas (atariage.com).  They make good products but sometimes get bogged down in shipping, especially during the holiday rush.  Most of the games listed below are $40-$50 with the box option.

If given the option of NTSC or PAL, please choose NTSC.

Conquest of Mars

With box.  Available at AtariAge.

Crazy Balloon

With box.  Available at AtariAge.

Draconian

With box.  Available at AtariAge.

Gunfight

With box.  Available at AtariAge.

Ladybug

With box.  Available at AtariAge.
RealSports Volleyball

With full-color box and manual.  You can find this for cheap on eBay; don't pay over $20 for it.  At the time of this writing, there's a used copy for $6.99 including shipping, another used copy for $9.99 including shipping, and a new copy for $16.99 [or best offer] including shipping.