Some of the sources for insurance for photograhers, specifically, are professional organizations like the ASMP and the PPA.  Take a look at this link for ASMP, you can get an idea of what kind of coverage you can get at a group rate by becoming a member.  This is likely the most comprehensive list of coverage for photographers, not everyone, and in some cases, nobody else can offer this kind of coverage.  Here's a list of what they make available, for coverage:

OFFICE CONTENTS: Covers business personal property that is situated within your office such as furniture, computer equipment, copy machines, fax machines and improvements & betterments.

MISCELLANEOUS EQUIPMENT: Protects your cameras, lighting, computer equipment outside of your office and darkroom equipment against fire, theft, water damage, breakage, earthquake and much more. Coverage is worldwide and on a replacement cost basis for owned equipment. This differs from some policies that exclude coverage for theft from unattended vehicles, earthquake, that are limited to the United States and Canada or only provide coverage on a depreciated basis.

The ASMP Prosurance policy automatically includes a $35,000 limit for rented equipment including Hired Automobile Physical Damage (See Below). This limit recognizes the growing trend to rent versus own equipment and the high cost of digital systems. The valuation for rented equipment is legal liability and actual cash value for hired vehicles. The standard deductible is $500 but a $1,000 option is available.

HIRED AUTOMOBILE PHYSICAL DAMAGE: Protects against physical damage to rental cars with a limit of $35,000 for any one vehicle subject to a $500 deductible. Coverage is Worldwide. (This coverage is included as part of rented camera equipment section of the policy. One limit applies for both vehicle physical damage &/or rented camera equipment.)

NEGATIVE FILM & FAULTY STOCK, CAMERA & PROCESSING - $15,000 LIMIT: This coverage pays for expenses to re-shoot the job due to lost, stolen, damaged film or digital imagery &/or film rendered unusable as a result of laboratory processing errors and/or camera malfunction. Coverage is designed to cover a current job and you must actually re-shoot the job in order to collect under this policy section. This important coverage is provided on a worldwide basis. Losses resulting from operator error are not covered. The standard deductible is $500.
Imagine that your camera bag were to be stolen after a shoot. The loss suffered would be greater than just the value of your actual camera equipment as you may have also lost exposed film and/or a digital storage device. If your camera were to malfunction, you might lose some or all of the images from the shoot or they may be unusable. These are a couple examples of claims that would be covered under this section of the policy. Please note, this coverage section does not cover stock photography or the liquidated damage amount of $1,500 per image.

PROPS, SETS & WARDROBE - $25,000 LIMIT: Protects you for damage to or theft of other people’s property that is in your care, custody or control and is a part of your photographic set. There is a $10,000 Sublimit for Jewelry, Furs, Fine Arts, Antiques, Precious Metals and Objects of Art. The standard deductible is $500.

EXTRA EXPENSE - $10,000 LIMIT: Covers the additional expense incurred to complete your photo shoot should your cameras, props, sets & wardrobe and/or location sustain direct damage from a covered loss. Coverage has been extended to include mechanical breakdown of cameras, generators and computerized systems to control cameras. The standard deductible is $500.

THIRD PARTY PROPERTY DAMAGE - $1,000,000 LIMIT: Protects against unforeseeable damage to a location in your care, custody & control while the location is being used temporarily as part of a photographic set. The standard limit is $1,000,000 and the standard deductible is $500.
BUSINESS INTERRUPTION: Covers the actual loss sustained for up to twelve (12) months as a result of direct damage to the premises listed in your policy by a loss from an insured peril.

PORTFOLIO AND CASE - $2,000 LIMIT: This coverage protects the cost to reproduce prints, slides, chromes, tear sheets, etc. The basic policy provides up to $40 per image if your portfolio were to be destroyed, lost or stolen. Coverage is worldwide. Note, this coverage section does not include stock photography. The standard deductible is $500.

MONEY & SECURITIES - $10,000 LIMIT ON PREMISES / $2,500 LIMIT OFF PREMISES: Covers loss of money & securities resulting directly from theft, disappearance or destruction.

GENERAL LIABILITY - $1,000,000 LIMIT: Protects you for your legal liability against lawsuits for bodily injury or property damage that occurs within the United States and Canada. (Note: There is limited worldwide liability coverage.) One of the important aspects of this coverage is that it affords coverage both on your premises and locations within the policy territory. Listed below are some of the important coverage exclusions.
a.      Injury to people deemed to be covered by a Workers Compensation Statute.
b.      Benefits payable under a statutory disability statute.
c.       Anything having to do with the use, loading or unloading of an automobile, watercraft, or aircraft.
d.      Damage to other people’s property in your care, custody or control.
e.      Claims resulting from an improper model release, invasion of privacy, infringement of copyright or trademark, infringement of patents, or libel or slander if you are in the business of advertising, publishing, broadcasting or telecasting.
f.       Claims arising outside of the United States or Canada.
g.      Anything having to do with pollution.
h.      Any intentional act.
i.        Wrongful termination, discrimination, or sexual harassment

NON-OWNED & HIRED AUTOMOBILE LIABILITY - $1,000,000 LIMIT: Protects an employer for bodily injury or property damage claims that arise from use of a hired, borrowed, or rented vehicle. This coverage will respond only after the policy insuring the vehicle involved in the accident has paid its limit. Please note there is no coverage for a person who drives their own vehicle on your behalf. Coverage is limited to the United States and Canada.

ERRORS & OMISSIONS LIABILITY - $1,000,000 LIMIT: For those members who meet the eligibility guidelines and complete an application, coverage can be extended to include copyright infringement claims as a result of errors and omissions. An important policy enhancement for this type of coverage is that the defense costs are in addition to the policy limit. (This is an optional coverage and subject to an additional premium.)

LOSS PAYEE & ADDITIONAL INSURED: A Loss Payee is a person or organization that has a financial interest in the property given or leased to you and for which you have agreed to provide the insurance. By adding a Loss Payee endorsement, both signatures are needed on a claim check in order to cash the check. The loss payee thereby maintains control of the insurance claim proceeds.
An Additional Insured endorsement extends your liability policy to cover another person or organization for bodily injury and/or property damage claims resulting from your negligence. Since the insurance carrier is now protecting more than one business or individual, there may be an added premium for this coverage.

Now, you get this coverage through ASMP at a significantly lower rate than if you put together the coverage yourself- in fact, many agents would be unable to offer you some of this coverage.  It's straight economy of scale.  You bring enough to the table, in terms of subscribers, and it's worth it for the company to create the coverage.  The PPA list is likely pretty similar, but they don't make that information available to non-members.