The single largest cause of disappointment with a first telescope is the gap between the pictures used to sell it and the view through the eyepiece. This page is what the eye actually sees, aperture by aperture, so the instrument arrives with the right expectations attached to it.
What every telescope in this index will show
Even the smallest, a 76mm reflector at $79.95, shows lunar craters in sharp relief along the terminator, the phases of Venus, the four bright moons of Jupiter as points strung out in a line, and Saturn's rings as an obvious ellipse rather than a circle. Those four sights are the ones that make people gasp, and none of them needs aperture.
What the eye does with the planets
Saturn through a telescope is small, sharp and pale yellow, and the rings are unmistakable at 50x in almost anything. The photographs that sell telescopes are stacked from thousands of video frames, and no eye sees that. What the eye does have is resolution in moments of steady air: watch for a few minutes and the image will snap into clarity for a second or two at a time, and that is when the Cassini division and the belts on Jupiter appear.
What changes when the aperture grows
Faint objects are where aperture pays. At 76mm the brighter clusters are patches of haze with a few stars; at 130mm a globular cluster starts to grain at the edges; at 200mm it resolves into hundreds of individual stars and the brighter galaxies show a shape rather than a smudge. Colour is the exception: except in the brightest stars and planets, the human eye sees deep sky objects in grey no matter what you spend.
Questions people ask about telescope
What can you see through a telescope?
The moon in detail, the phases of Venus, Jupiter and its four bright moons, Saturn's rings, star clusters, double stars and, with more aperture and a dark sky, nebulae and the brighter galaxies.
Why does Saturn look so small?
Because it is, at any sensible magnification. It is also sharp and unmistakable, and most people find the smallness part of the impression rather than a disappointment once they have seen it themselves.
Will I see colour?
In the planets and the brighter stars, yes. In nebulae and galaxies, almost never: they are too faint to trigger the colour receptors in the eye, which is why they look grey through any aperture.