While the Bond movie guns are interesting, the variety in the novels are even more so. Bond's choice of weapon seems to change depending on which author is writing the novel.
In the original Fleming novels (the best IMHO), Bond uses the Beretta 418 .25 Auto up until Dr. No when he is issued both the Walther PPK 7.65mm (.32 Auto) and S&W Centennial Airweight (Model 42) in .38 Special. Bond carried the Walther regularly and switched to the more powerful S&W only when he was expecting gunplay (Fleming obviously wasn't a gun person as a larger, heavier revolver would have been better suited to that role than a lightweight J-Frame).
The reason that Fleming switched Bond's guns was because of correspondence with a fan named Geoffery Boothroyd who was also a gun enthusiast. Fleming originally chose the Beretta 418 because he'd been issued that same sort of gun while working for SOE during WWII and thus thought it a suitable gun for a spy. Boothroyd pointed out to Fleming that the .25 Auto offered very little power and thus was a very poor choice. Boothroyd further suggested that Bond switch to the then-new S&W Centennial Airweight but Fleming replied that he preffered the character to use a semi-automatic, thus Boothroyd reccomended the Walther PPK. It was because of this advice that Fleming also introduced a new character to the Bond series: a quartermaster named Major Boothroyd but better known to the world by his codename "Q".
John Gardener had bond use a variety of weapons including some unusual choices like the Ruger Super Blackhawk .44 Magnum that Bond kept as a "car gun" (the car was a Saab 900 turbo in that particular novel) and the rather long-in-the-tooth Browning Model 1903 in 9x20mm Browning Long (Bond even remarks about what a dated gun it is in the novel). However, Bond's most common weapon throughout the Gardener novels seems to be the ASP 9mm which, when one thinks about it, is a rather logical choice for a spy as it offers both reasonable compactness with reasonable power.
Raymond Benson's choice of weapons for Bond seems to correspond with the films: he first arms Bond with the then-iconic Walther PPK but later switches to the Walther P99 with Bond sometimes switching back and forth between the two in the same novel (the P99 is sometimes used like the S&W M42 in the Fleming novels). Probably the most interesting Benson novel, from a firearms perspective, was Doubleshot. In that novel, Bond uses both the PPK and P99. The PPK was loaded with Glaser Safety Slugs in an attempt to increase its effectiveness and the P99 was traded up for a .40 S&W variant rather thant the more common 9mm.
