Mars begins the month in Virgo but crosses the border into Libra on the 10th. The planet starts out the month at magnitude +0.4, but dims to +0.6 by the 31st. Its view through a telescope is disappointing, as it shrinks from 8 arc-seconds to 7" wide during August.
Not so its neighbor Saturn. In fact, the two approach each other quite closely this month. Mars and Saturn lie within 4° of each other from the 20th to the 29th. Their closest approach occurs on the 27th, when Mars lies just 3.6° from Saturn. By then both will be of similar brightness - magnitude +0.6. Brightness difference aside, can you tell them apart by their color? Mars, of course, is reddish; Saturn should appear yellow-white. Certainly, though, as seen through a telescope, they could not be more different. Saturn's disk is about 16" in diameter, with its magnificent ring system stretching 36" across. And, in contrast to the two moons of Mars - which are tiny and beyond the reach of most amateur telescopes - Saturn boasts a full retinue of satellites, up to half a dozen of which may be visible in larger scopes.
Neptune reaches opposition on August 29th, which means it's at its closest, brightest, and largest of this entire year. For this remote planet, though, that is not saying much. The planet is almost 2.7 billion miles from us, shines at a feeble magnitude 7.8, and displays a disk no more than 2.4" across in a telescope. In smaller scopes, it may be difficult to distinguish from a star.
Neptune's sister "ice giant," Uranus does slightly better. It rises about an hour and a half after Neptune, in the constellation Pisces. Even though it is not yet at opposition and therefore nearest to Earth, it is "only" 1.8 billion miles away. It is therefore brighter; at magnitude 5.8, it may even be within naked-eye range from dark sky sites. In a telescope, it displays a clear greyish-green disk about 3.6" wide.
Venus rises just 2 hours before the Sun at midmonth, and it barely climbs out of the morning twilight before sunrise. It shines at "just" magnitude -3.8 - its faintest for the year. It gains some slight altitude during the month, rising from 7° to 12° at sunrise during July. In a telescope, its nearly-full disk appears only 12 arc-seconds in diameter.
Mercury goes through superior conjunction - passing "behind" the Sun from Earth's point of view - on August 8th, and slowly begins to climb into the evening sky. You're unlikely to see it at all, however, unless you have a clear view low to the western horizon shortly after sunset. For Northern Hemisphere observers, this is the worst evening appearance of Mercury of the year.
Perhaps the most remarkable of planetary sights this month occurs in the morning sky, low in the east before dawn: a conjunction between Venus and Jupiter. During the first half of August, Venus rises first, about an hour and a half before the Sun. Jupiter follows about a half hour later. But day by day, they get closer. On the morning of the 18th, only 15 arc-minutes - or about half the width of the Full Moon - separate them. Venus, at magnitude -3.8, will be the brighter of the two; Jupiter will muster a magnitude -1.8. Both should be visible in the same field of view of the average telescope. Venus will display an almost full disk about 10" across, while Jupiter will be 32" across. However, don't expect to see much detail in any case; the two will be quite low in the predawn sky, and morning twilight will be approaching. Following the conjunction, Venus and Jupiter "pass" each other in the sky, and for the rest of the month, it will be Jupiter that rises first.
The dwarf planet/asteroid 1 Ceres and the asteroid 4 Vesta are about 3° apart, in the eastern part of Virgo.
Pluto is just past opposition, so this is a good time to try to search for it. You'll need a large telescope and detailed star charts. It shines no brighter than magnitude 14.1, and is in rich star fields in Sagittarius.