I have to agree with Instapundit and Sarah Palin that going third party should be a last resort, not something that should be a standard approach by the Tea Party. A far better idea is to filter in at the ground level and influence the next generation of politicians. The target has to be the GOP which is at least nominally aligned with Tea Party ideas, in contrast to the Democratic Party which is irreconcilably oppose.
In general, the most realistic option for third party politics is to be destroyed by having your platform stolen by a major party. It may mean a local defeat but if the real goal is policy implementation that’s not so bad. Still, I strongly support cross listing ballots so that third parties can endorse major party candidates. I think that gets the best blend of the benefits of parliamentary politics and our first-past-the-post system.