a circle -- unity, harmony, never-ending, immortal

Pentagram, and Pentacle -- a pentagram is a five pointed star; a pentacle is a five-pointed star within a circle; this is the symbol of magick and Witchcraft in general; four of the points represent the elements (earth, air, fire, and water), and the top represents Spirit, and the spirit within a human, and the circle is usually unity or harmony

the Inverted Pentagram -- five-pointed star with two points facing upwards; this is actually a symbol of the benevolent Horned God, His horns showing his connection with animals and Nature, despite what some movies have made of this symbol; some Satanists use the symbol, but any symbol can have many meanings; the Swastika (equal-armed cross with each arm bent at a right angle) was a symbol for sun-gods for many millenia, or thousands of years, before it was adapted for the reason people recognize it, today (the Nazi regime); it's really kinda sad that people use symbols for things that will leave a negative effect on the image of the symbol; if you start some movement, make up your own symbol and be more original

Ankh -- (pronounced "onk", with an "ah" sound, as in, "turn the light on"; a one syllable word) ancient Egyptian symbol; a looped cross, i.e., a cross with a loop at the top; also called the Crux Ansata; symbol of Life; symbol of cosmic knowledge, health, wholeness, rebirth, sexual intercourse, immortality, eternal life, and sacred to many gods, such as, Isis and Osiris

the Tau -- the sacred cross, very ancient, looking originally something a "T", though, most any sort of cross has been drawn; symbol of eternal life, soul purification, promised goodness, health, knowledge, self-sacrifice (not necessarily death, but definitely symbolic, too, of the "sacrifice" of the crops to have food during the winter), etc.; symbol of sun-gods, and of the Divine Son/Sun god, also; very ancient, very Pagan

the solar cross -- an equal cross, or like a plus sign "+", within a circle; symbol of the five elements, and of the power of the sun

the sacred triangle -- symbol of unity, and of the spiritual, physical and mind, in unison, or of Goddess, God, and Divine Son, or various trinities; connected with the sun-god, and the power of the rays of the sun; can be used to draw down and focus power into a certain object (if you form the sacred triangle with your fingers/hands)

the Ouroborus -- the symbol of a serpent swallowing it's own tail; a symbol of eternal life, and the never-ending

Infinity symbol -- like a figure-8 lying on it's side; symbol of infinity, eternity, and of working between the physical and spiritual worlds

a square -- involved with the physical plane/world/level; something grounded, or more solid; or the four elements

the trapezoid -- symbol of magick, generally higher magick or more ceremonial; the tops of altars are sometimes made to be in trapezoidal shape

the pyramid -- enlightenment, the New Age, meditation, power, the sun, Ascension

the Eye of Horus -- the All-seeing Eye, the protector, the destroyer of negative powers, the watcher; associated with the Moon, symbolically, also, and the air element

Goddess and corn symbol -- a goddess figure holding aloft an ear of corn; here, whatever she's holding represents her Divine Son, who is usually the sun and harvest god, who also represents purification, spiritually and physically; so, i.e., her holding an ear of corn (or what have you) is the same as her holding her child-son on her lap (which is one of the oldest and most venerated [receiving adoration] symbols/pictures/images/statues); and if she's holding up a flaming torch, it represents Her Son is the Light of the World, or Lux Mundi, and that representation means, among other things, enlightenment, and purification of the soul and actions, and therefore, freedom

the crown -- guess what, it's a symbol of power, like the horn is a symbol of power, or sometimes of dignity, or even fertility; the same with wings, like a lion with wings (sorta like the Sphinx, though, that has deeper meanings), representing the "mighty ones," sometimes the Ancient and Shining Ones (the Gods), or occasionally, people, or leaders, or founders, fortifiers, etc.

the phoenix -- a mythological creature; the bird of fire which burns up into ashes at night, and is reborn the following morning, from the ashes; a powerful, mystical symbol; also a fire element symbol; stands for rebirth, regeneration, life from death, "life from out of the ashes," sometimes the New Age, new life coming from the destruction (which becomes your foundation for the new life, then) of old bad habits, or things no longer needed/useful; like, the old soul in a new package; the tears of the phoenix are said to have healing powers; interesting water from fire metaphor; also, the pure Light

the six-pointed star -- formed from two triangles, so, lots of power, there; symbol of unity; called, also, the creator's star; there are seven, eight, ten, four, and what have you, -pointed stars, also, that have their own meanings and purposes

a sigil: a sigil is a designed symbol (which is enjoyable to do), sometimes from drawing lines starting from certain points, like a chart with 9 numbers (and 9 squares, therefore), and using numerology, or from combining other symbols, or letters, etc.; can act as a seal on something; can be used as an image to summon a deity or spirit; can act as the Name of a deity or spiritual entity; or, used as a very personal logo, or as a signature, and so forth

* And Yes, there's many more symbols in the world, and you can form your own. :-}