Since it's the first slime mold to appear on BPotD, I was really hoping to have a superior photograph, but a passable one will have to do. I'm fairly certain this is Fuligo septica, one of the few of these fascinating organisms to have a well-used common name – dog vomit slime mold. Slime molds are not true molds; true molds are fungi, while slime molds are protists. Wayne Armstrong has an excellent article on slime molds that explains how slime molds are different from other organisms. He also illustrates the common name through a series of Fuligo septica photographs. If you read his account, you'll learn that this yellowish mass is the spore-bearing stage in this slime mold's life cycle, known as the aethalium.

Two other resources on this species are Tom Volk's Fungus of the Month for June 1999 featuring Fuligo septica (note that Tom states in the first sentence that it isn't a true fungus) and images of Fuligo septica from CalPhotos.

A few broad resources on slime molds, if you'd like more detail, include Wikipedia, a gallery of Myxomycetes (beautiful!) and “Hunting Slime Molds”, an article from Smithsonian Magazine (but only the first two pages work, unfortunately).

In BPotD and other news, one more day until the small announcement...

Biology resource link: An extremely worthwhile project, Discover Life “provides free on-line tools to identify species, share ways to teach and study nature's wonders, report findings, build maps, process images, and contribute to and learn from an encyclopedia of life that now contains 279,352 species.”