Of the few "cash for offers" sites I've tried, Inbox Dollars is the only one I've stuck with. The others didn't have as many different ways to get rewarded, so the earnings added up so slowly, it seemed it would take a lifetime to earn the minimum payment amount even once.

Here's a breakdown of all the reward methods you get at Inbox Dollars...

Emails - On average, these pay 3¢ each, and you receive normally from one to three of them per day. Unlike some other sites of this genre, the process is very fast -- two clicks and you're credited (in some cases, only one click). No need to log in, and you don't have to view an ad for a certain number of seconds either.

Surveys - Earn $1.00 for each survey you complete. There are also a few "profile surveys" (questions about your household, interests, etc.), which are much shorter than the other surveys and pay 25¢ each.

Offers - There's always a good selection of 100% free ones. There are several offers paying $1.00 each for joining sites that pay you to take surveys, for example. There was an offer that paid $3 for signing up for a free prescription discount card... Registering with MyCokeRewards paid 50¢, taking a test which calculates your "Real Age" (with awesomely detailed recommendations based on your results) also paid 50¢... Then there are free trials offers, which pay even if you decide to cancel before the trial ends. And lastly, there are the offers which require upfront payment, whether one-time or recurring... so essentially, you get a rebate for trying a product or service which interests you, which is the same as the next reward method:

Shopping - Use Inbox Dollars to save money at places you already shop online. Get cash back (up to 40%) on purchases from over 600 popular online stores. They include Target (5%), Overstock.com (2.5%), Buy.com (2%), Family Christian Stores (3%), Hallmark (7%), and many, many more.

Games - You have to be a serious online gamer, as this requires depositing money to compete for cash against other players. For each dollar you deposit in your games account, they say you earn about 5 cents in your Inbox Dollars account.

Referrals - For each person you refer who stays an active member long enough to earn their first payment (when balance is at least $30), you get a bonus $5. You also earn a (very) tiny commission (like .001¢ per email) for the paid emails your referrals read. As of Jan. 31 2008, they've vastly improved their referral system. They now pay you 10% of all your referrals' earnings, and it's credited to you instantly.

Membership - Everyone gets $5 to start them off as soon as they sign up.

Sweepstakes - Since December 2007, they've been doing monthly sweepstakes giving away some sweet prizes to some lucky winners. In the current (March) contest, you earn entries for each cash offer you do, and the top prize is a choice of a Dell Laptop or an LCD TV along with a Nintendo Wii. Additionally, they're giving $25 Restaurant.com gift cards to 25 other entrants.

Gold Membership - Previously, this was something you had to purchase for a one-time fee, but now they're giving it automatically when you earn your first payment. What you get by being a Gold Member is:
~~More Referrals - "Every time a new member joins InboxDollars without being referred by an existing member, they are placed into a pool of non-referred members. Your Gold Membership guarantees you a portion of the members in this pool of new non-referred members."
~~Faster Payments - "Your check payments will be processed 3-9 days after your request rather than within net-30. Any time you request a check payment during the week, it will be processed on Wednesday of the following week and mailed promptly."
~~Double Sweepstakes Entries - "Your Gold Membership gives you an additional Sweepstakes entry for each entry you earn while participating in our Sweepstakes. This doubles your chances to win!"

You'll probably want to get a separate email account to use for Inbox Dollars and any sites you sign up with through them.

One other piece of advice: You can request a check any time after your account balance reaches $30, but for each check they send you, they deduct a $3 processing fee, so to make that not as big of a cut, just wait til you have a higher balance - say, $50 - to request a check. I didn't think about it til after I'd requested my first check: