It is standard practice in recent years that an hour bonus should have 40-60 questions, though some contests have strove to increase or decrease that number. There has been greater variance on supers, with the numbers of questions ranging from 100 to over 300. The better-received supers tend to have around 125-175 or so.
Be sure to cover a variety of different genres of popular and high culture in your bonii. In particular, you should certainly cover television, film, and popular music. Once upon a time, it was traditional to have a sports bonus, but as the people winning contests have known less and less about sports, this tendency has almost vanished. Other topics that are often covered by either entire bonii or parts of bonii are games, fine arts, literature, history, and the sciences.
Audio Bonii
An audio hour bonus should be composed of 40-60 song clips on some kind of theme, of your choosing. A theme can involve similar lyrics, similar instrumentation, the relation of a narrative (e.g., The Wizard of Oz audio), etc.. The length of clips can be varied, but try to have each clip last a second or two; a series of half-second clips is usually unidentifiable by anyone.
While every audio bonus will bear the fingerprints of the creator(s), attempt to have a range of music for varying tastes. Make sure you have a distribution of popular music representing each of the last six decades, though you should emphasize the music of the last 15 years. Be sure to cover classic/current pop, rock, R&B, hip-hop, country, indie/alt., and singer-songwriter folk.
There are traditionally two audio bonii. However, if you have a non-audio music bonus or if you have an audio super-bonus, you may wish to reduce this number. Likewise, it can be increased if one audio bonus is something non-musical. For that matter, you don't have to have one at all if you don't feel like it.
Audacity is a particularly good tool for assembling audio bonii.
Visual Bonii
While not as sacred as audio bonii, the majority of recent contests have had visual bonii of some kind. These usually represent television, film, and fine arts, but are not limited to these.
There are three major types of visual bonii. The first requires taking a group of separate pictures and individually asking questions about each, typically basic identification of the source. A recent example is the Movie Stills bonus.
The second is the collage. This involves creatively integrating the visuals into one, and having teams identify the component pieces. A recent example is the Animation bonus.
The third is the video. This is similar to the audio bonus, but with video clips. Since it can be freeze-framed, there is less of an impetus to keep the video clips long, but clips of less than half a second are still irritating to identify. This is the most difficult and rarest type of visual bonus. The DVD "Just Say No" bonus (composed by ripping DVD chapters with AoA DVD Ripper and editing them with Blaze Media Pro) is a recent example.