If you want to build new widgets using biology, you need to work with cells amenable to the task. Tom Knight, at MIT, prefers the innocuous insect commensal bacterium Mesoplasma florum as a prototype biological chassis and power supply for genetic circuits.
After reading my article on garage biology in this month's Wired, David Metzgar, at the Naval Health Research Center, sent me a paper describing another candidate organism, Acinetobacter ADP1. The paper describes ADP1 as naturally competent for genetic transformation and that it has a "strong natural tendency towards homology-directed recombination." That is, it likes to harvest DNA from its environment and incorporate it into its genome. Metzgar writes that, "The close relationship between E. coli and ADP1, combined with the newly available whole genome sequence of ADP1, allows the tremendous amount of existing knowledge related to gene function and metabolism of E. coli to be applied directly to ADP1." They ported a variety of genes directly from coli to ADP1 without modification.
Since it is common, easily grown, and poses no pathogenic threat to humans, this could be a useful bug.