Ally, CapitalOne360, Barclay, and SmartyPig all tend to have the highest rates. I think SmartyPig is the highest at 1%.
You can earn 5% with Mango, but getting the money out is difficult and there is a cap of $5k. Probably not worth it.
There are various credit unions that provide 2-3% if you swipe their debit card enough times per month. I'm not a fan of debit cards so I can't point you to one, but I know they exist.
You could go iBonds or CD's for higher interest, but then you have penalties upon withdrawal and are slightly less liquid.
Other than that, you won't find a liquid account much better than that.