Does anyone know when the Tax Rebate Checks will be mailed out? Will they be mailed out according to social security number or last name? Also we filed married filing jointly with 4 children listed as dependents and our income was under $50K, approximately how much would our rebate check be?

Checks are expected to be sent in May. I've not heard any specific plans for how it will work, whether by SS no, or region, or alphabetically, or whatever.

Your amount should be $2400 - that's $1,200 for married filing jointly plus $300 for each child. This assumes that your 2007 tax bill was at least $1,200.

Here's a web site from the IRS that's pretty helpful:
Economic Stimulus Payments Information Center