Regarding interest rate spreads, QE2 is your friend until the end. Check out the yield spread between the AAA GO 10y Muni Bond Index and 10Y Treasuries. AAA 10y Muni's yield 2.65% and 10y Treasury Notes yield 2.51%, a 0.14 spread. The municipal bond index is from Municipal Market Advisers.
Snapshot of AAA General Obligation 10y MMA at Bloomberg.com
AAA 10y GO Muni Bond Index Yield / 10y Treasury Yield (10y at Bloomberg)