SponsoredTweets offers a unique service summed up as this: Khloe Kardashian tweets about you for $13,000.
Of course, there are other options, like CPC advertising where people would volunteer to tweet your message and you pay them per click.
The bad news? Clicks are mostly bogus.
The horrible news: SponsoredTweets will scam you, siphoning funds from your account.