Strength

The radioactive spider that bit Peter transferred its characteristics into his 'puny' DNA. Among these was the proportionate strength of a common house spider. His enormous spider-strength allows him to lift or press 10 tons or more (if he's under stress), and perform all kinds of life-saving feats (including lifting buses and shielding little kids from falling debris.) His strength also helps him crash into Four Freedoms Plaza whenever he feels like it.

Spidey's might makes him deadly in hand-to-hand combat, which is his main form of direct attack. He uses strength with his spider-sense and speed in combat, making him extremely hard to surprise, harder to hit, and even harder to withstand. Spidey can go toe-to-toe with a lot of villains in the Marvel universe, and has even held his own against the Hulk from time to time (without the Captain Universe power, even).

His incredible physical power gives him great endurance, and also helps him take lots of damage. This, coupled with the Parker determination, makes him virtually unstoppable!

Speed

As well as gaining the strength of a spider, Peter also inherited the arachnid's swift speed. He can move and react several times faster than an ordinary human. His reflexes allow him to dodge a bullet (if far enough away), and coupled with his uncanny spider-sense, gives him a definite advantage in dangerous situations. Very rarely is Spider-Man surprised or unaware in a fight, now matter how sneaky or devious the villain is.

Grip

Spider-Man's most helpful ability in his crusade against evil is the Spider's natural ability to walk on walls and ceilings. When Peter was leaving the laboratory experiment where he was bitten, he walked in the path of a car. Out of fear, he leapt into the air and attached himself against the wall of a building. Spider-Man is at home on the sides of skyscrapers in New York, and this unique power lets him crawl pretty much anywhere he wants.

His spider-grip lets him get into all kinds of places, like air vents and elevator shafts. He often uses his "grip" to hide in corners and on ceilings, dropping in at the most opportune time. His ability to adhere to surfaces helps him avoid deadly falls as well. Spidey can attach himself to basically anything, including moving objects like trucks and the bottoms of bat-gliders. He can also use this power to hold objects and things.

Spider-Sense

This ability has saved Spidey umpteen million times in the heat of battle. It is an extended danger sense, and it gives Peter an itching feeling at the base of his skull whenever danger is near. The scope of this power is enormous, and aids him in both everyday and combat situations. The sensation this power gives him helps him to 'focus-in' on the source of the danger. It acts like radar, guiding him if he's stricken blind , or plunged into darkness.

Spider-Man's sense also warns him of potential danger, such as a hidden weapon or a disguised enemy. It alerts him of other types of danger as well, including times where his secret identity is at risk, or crumbling ceilings, creaky floors when he is trying to be silent. His spider-tracers run on the same frequency as his spider-sense, freeing him from having to use a tracking device. His Spider-Sense will warn him of all threats, even those that are not particularly deadly (snowballs, swatting brooms, etc.).

As mentioned above, the greatest advantage of the spider-sense is that it is used in conjunction with his other abilities. Most times Spider-Man can react on instinct alone, helping him to avoid a barrage of bullets or other rapid attacks. Often, he doesn't even need to think about impending danger, his reflexes will do the job for him.