personal opinion , no offense .
first of all wiak is right , you can't use DDR-3 with AMD's current offerings and if you want to use DDR-3 and buy AMD processor you should wait till 09 and buy AMD 8 series of motherboards which are AM3 compatible.
plus i think that buying DDR3 right now isn't resonable , cause you can buy DDR2 quality memory at nearly no price , they're so cheap that we should say memory makers are giving them away for free
, on the other hand you'll have to pay about five times of the price of the DDR2 for quality DDR3 memory , which you'll gain about 5% or less performance improvement , you also have to buy a pricey DDR3 motherboard as well which will cost you about 1.5 times of a mature DDR2 motherboard , plus DDR3 isn't mature enough you'll end up gaining nearly no performance because of high latencies of DDR3 memory .
i suggest you to take a look at Aanandtech's http://www.anandtech.com
comparison between DDR2 and DDR3 before considering any purchases.
by the way don't wait for DDR3 on AMD.