Update: Links still working as of 21 April 2012.
There was a great offer for a Chase Southwest Signature Visa that nets you 50,000 miles after your first use, up to 15,000 points for balance transfers (which is a pretty unique benefit), plus 6,000 miles every year on your cardmember anniversary that was set to expire on 7 Aug 2011. The offer is still active and you can continue to apply via the link here for the personal card and the link here for the business version.
The 50,000 miles, if used efficiently, can get you about 3 round-trip tickets. If you get both the personal and the business versions, then spend $10k (or earn 10,000 more points through flying), then you can also get a companion pass valid through the end of the following year. That’s pretty worth it for a credit card signup with no minimum spending 🙂