There's an interesting Ruiters article discussing the lack of collectivity value mass produced memorabilia, anything sold in an infomercial will never reach the level of scarcity that is key to a collectible's value. A Smithsonian curator in the article clarifies "Anything that's made to be collectible is not"
Consider most of the items below for their sentimental value, but not as financial investments.
(Click images for a detailed view)
Limited edition works by Jonas Perkins
barackobama.com still offers a variety of merchandise at clearance prices, including lots of mugs, buttons, shirts and a little jewelry. Checkout the "Runway to Change" section. The original artist's poster designs appear to be all sold out.
obama-bling.com (no connection to this site) has additional democrat designs, in addition to the obama specific jewelry.
Other Presidential Memorabilia may be found at about.com