Although there is not complete consensus on this issue within the 9/11 truth movement, here is a collection of articles, many of them by Jim Hoffman, arguing that the WTC buildings must have been demolished using explosives. Plus a few past milestones on the evidence. Judge for yourselves...

Offsite:

Taking a Closer Look: Hard Science and the Collapse of the World Trade Center
by Dave Heller, physicist, architect and builder, in Garlic & Grass

The Collapse of Seven World Trade Center (from wtc7.net)

The Twin Towers' Destruction (from 911review.com)

"Building a Better Mirage. NIST's 3-Year $20,000,000 Cover-Up of the Crime of the Century." Responds to the official final report on the WTC collapses by the US National Institutes for Standards and Technology (from 911research.wtc7.net)

Rise
Powerful music video on the WTC collapses hosted by bushflash.com; includes TV commentators speaking of explosions.

Onsite:

Popular Mechanics Attacks Its "9/11 LIES" Straw Man by Jim Hoffman (See also: Popular Mechanics' Deceptive Smear Against 9/11 Truth. Very comprehensive, illustrated treatment.)

UL Executive Speaks Out on WTC Study (Kevin Ryan)

UL's Letter Disowning Ryan and 911Truth's Response

Ongoing Developments: the New York tapes
Researchers Comb Through First Responders' Tapes and Testimonies

Older Puzzle Pieces:

9/11/01: NY Fire Department chief of safety [Link no longer live] (video) told TV reporters there were "bombs" and "secondary devices," which caused the explosions in the buildings.

Military contractor Van Romero says explosives were planted in towers - later retracts (Sep 2001)

Fire Engineering Editor Bill Manning decries destruction of Ground Zero evidence (Jan 2002)

Silverstein on WTC 7: "Pull It" (2002, first noticed by researchers in early 2004)

The history of WTC 7 - headquarters to CIA, SEC and OEM, compiled by John Horne

Blackstone Group, owner of WTC 7 mortgage (sort of like The Carlyle Group, but possibly worse)