In the US
Liberals = Democrats
Conservatives used to = Republicans
The Republican nominee is currently Senator John McCain.
McCain has made his career on being a self-proclaimed "Maverick" that bucks the system and does what he wants to do. In the recent past, he forged a bill called McCain-Feingold (co-authored with senator Feingold) that placed severe restrictions on not only where money comes from in a political race, but also how organizations can advertise 6 weeks before an election. It in effect limits the freedom of speech. Conservatives view his bill (now law of the land) as an assault on free speech. Democrats just found ways around the law, and created new organizations that slipped through the loopholes. Republicans followed suit.
McCain was chosen as party nominee because of the way our Primary Elections work. Each state gets to chose when it will hold its primary, and who can vote in the primary. The states in our more liberals areas held their primaries in the early part of the year, and their lax rules about declaring which party you are affiliated with let a lot of so called "moderates" -- really liberal democrats -- vote for the guy in the other party (McCain - as a republican) figuring he'd be easy to beat in the general election in November.
This did two things: Gave McCain the momentum he needed to get rolling. Secondly, because these early "switch" voters crossed over to vote in the republican primary - they did not get to vote in the democrat side. (In all states, you only get to vote in one or the other party's primary, not both). Hence, Hillary Clinton lost some of her support (she was considered the "safe" candidate early on), and Obama started to gain momentum and inch ahead.
In the US, the labor unions usually side with the democrats, since the dems like to keep upping the minimum wage, and place tarrifs on imported goods. But the rest of the democrats policies are destructive to the labor unions. So there is a weird dichotomy going on with the labor/democrat marriage.
Conservatives in the US get mislabeled as the religious right. That's about as true as saying all Democrats are atheists. The so called religious right are a very vocal, but rather small minority in the conservative movement. Unfortunately, the conservatives don't have a voice in this year's presidential election, because our candidate was nominated by a combination of cross-over liberals and a minority movement in the republican party that is trying to distance itself from the religious right.
McCain may be a republican in name, and support of Ryan's favorite war: the war on terror

but most of his legislation that he's authored have been for liberal causes.
Hillary and Obama are both mainstream liberals, differing very little in their viewpoints.
Hope this helps!