The E4300 is great in that it has a low starting FSB speed. This means that you can get a motherboard that isn't all that great at overclocking, and still get a lot out of this processor. It also means that you can hit 3Ghz with DDR2-667 memory.
If 3Ghz is enough for you, then you can go ahead and get DDR2-667 memory. It's about $30 cheaper than DDR2-800 for a 2GB set. Here's the cheapest set.
Normally, we don't recommend going with the cheapest, but Kingston is a good brand, so it should be fine. But note that this processor performs significantly worse
when compared to rest of the family at the same frequency. The smaller L2 cache seems to me making a surprising 10%-15% difference in performance. Then again, processors aren't supposed to make a difference in games anyway. If you want more than 3Ghz from the processor, then get a DDR2-800
set. But its $30 more.
The Biostar TForce motherboard
($105) is a good budget overclocking motherboard. It also seems to fit your budget. If you want to go for a bit more overclocking headroom, however, check out the Gigabyte S3
($108). If you really want to get a good motherboard, then the Gigabyte DS3 P965 motherboard
($133) is the best you seem to be able to afford.
Crap, I'm starting to sound like such a salesman.