While we have many good things to say about all the efile providers we've reviewed, the one we most highly recommend this year is once again TurboTax. They are the #1 efile provider in the U.S. and provide an outstanding product which guides the novice and experienced taxpayer through the often humbling process of filing income taxes.
A close second to TurboTax is TaxACT which was independently owned until they were purchased this year by H&R Block. Their advantage is that filing your taxes with them is free, without qualification.
H&R Block is also a formidable presence in this space. They are still the #1 tax preparer in the U.S. thanks mainly to their tax storefronts, but they also provide a substabtial online tax package to accommodate even the most complicated tax return.