While it's always been possible to apply for credit cards online, I've had the devil of a time finding cards that matched my needs. For the longest time now I've been looking for one that had the best rewards program, because we use our card for pretty much everything (we also pay it off every month, which I highly recommend...if you can't do that, stick with cash). We've been getting a gas rebate, which has been nice with gas prices lately, but there's still a lot of things we use the card for that we aren't getting any reward for.
Think about the amount of money you spend each month. Now thing about channeling that money through a credit card that gives you something back in return. It's like free money. At least that's the idea, but finding a suitable card is tough.
I recently ran across http://www1.newcreditapplications.com/ , a web site that categorizes credit cards based on different characteristics, including the type of rewards offered. I discovered that 5% cash back was the most you could get, and that only for limited categories of spending. 1% was more likely if you wanted it to apply to all your spending. The Blue Cash card seems like the one I'll go with, since it has 5% back on selected spending (including groceries, a big one for us) and 1.5% back on everything else.
I have to stress that if you're going to use a credit card for the rewards, it only makes sense if you can pay the card off every month. Otherwise you're spending more in interest than you're getting back from the card.
This is one of the techniques we've used after our debts were paid off. If you're still in debt, read through the articles at Guardian-Tree.com for ideas on getting out of debt, and put off the new credit card for now.