I have several credit cards that I use for the rewards. I keep track of which cards have which offers going on at the time, and use them accordingly. I have no idea on interest rates for any of them, as I pay them all off monthly. None of these cards have an annual fee.
I'm not sure how much online shopping you do, but all of these cards offer online shopping bonuses - if you shop with various merchants through their site, you can get 5-20% cash back.
Many cards offer a sign-up bonus, like if you spend $500 within three months you get a $100 cashback bonus. My American Express, Citi, and Chase cards all did this.
American Express Blue Cash Everyday. You get 3% cashback on grocery purchases, 2% on department stores, 2% on gas stations, and 1% on everything else. Rewards can be redeemed for merchandise, gift cards, or statement credits at a minimum of $20 or $25. The online interface is fine, I don't mind it. It tracks how much you spend in the above categories, but it doesn't break them down any further than that. The one thing I've noticed about this card that's a little different is that it takes longer for the rewards to show up - it's one billing period "late", so to speak.
Capital One . My very first credit card. I get 1% back on all purchases, plus a bonus 1% if I pay my bill on time. You can redeem for a statement credit, a check, or gift cards with no minimum.
Chase Freedom. You get 5% back on rotating quarterly categories. For example, from October-December you get 5% back on airlines, hotels, Best Buy, and Kohls (nice for holiday shopping and traveling). From January-March you get 5% back on gas stations, drugstores, and Starbucks. You can redeem for merchandise, gift cards, statement credit, or a check with a $20 minimum.
Citi. You get 5% back on rotating quarterly categories. From October-December you get 5% back on Macy's, electronic stores, and toy stores. I just got this card in October, so I don't know what previous quarters were, and they haven't released the 2013 calendar yet. You can redeem for statement credits, not sure what the minimum is.
Discover You get 5% back on rotating quarterly categories. October-December is 5% back on online shopping and department stores. January-March is 5% back on restaurants and movies. They also offer a lot of bonus cashback offers. You get 2% back if you set up auto bill pay for phone, internet, and television. I got 2% back on everything during my birthday month. They'll announce periods of time (might be a day, might be a week) where they give 2%-5% back on all purchases. You can redeem for direct deposit or statement credits ($50 minimum) or gift cards ($20 minimum). They have a very nice online customizable spend analyzer that breaks down purchases into various categories.