I've placed the following sites in order based on how valuable I think they are. I considered the frequency of e-mails and the amount of money made from each site. This is something that I just started getting into, so more information will be available as I reach payout.
E-mail value: .1 to .5 cent per link (all cash)
Minimum to request payout: $5
Lots of e-mails! (as many as 50/day)
E-mail value: .25 to .75 cent per link on average, many point e-mails (but clearly marked and more useful than other sites)
Minimum to request payout: $45. However, you can upgrade your account just by earning points, and this will lower the amount.
INSANE number of e-mails! (100 to 200/day -- not enough time to click on them all!)
E-mail value: .25 to .5 cent per link (all cash)
Minimum to request payout: $1
Lots of e-mails! (25 to 30/day)
E-mail value: .25 to .5 cent per link (all cash)
Minimum to request payout: $1
Lots of e-mails! (50+/day -- be sure to have *bees helping bees* checked as an interest)
E-mail value: .5 to 1 cent per link (all cash)
Minimum to request payout: $3
10 to 15 e-mails/day
E-mail value: .5 cent (all cash)
Click on links on webpage once per hour: 3 cents each
Minimum to request payout: no minimum -- paid monthly
Few e-mails (2 to 3/day)
E-mail value: .5 - 1 cent per link (all cash)
Minimum to request payout: $5
Few e-mails (2 to 6/day)
E-mail value: varies from month to month (all cash)
Minimum to request payout: $10
Few e-mails (2 to 3/day)
E-mail value: .5 cent per link on average, some links only give points
Minimum to request payout: $8.50
Few e-mails (around 5/day)
E-mail value: .1 to .25 cent per link on average, many links only give points
Minimum to request payout: $10
6 to 10 e-mails/day
E-mail value: 1 cent per link (all cash)
Minimum to request payout: $5
Few e-mails (0 to 5/day), links expire quickly