Intel will be launching a cut-down version of it's P45 chipset which will go under the the name of P43 and it looks like it'll be quite a different chipset in more than one way. First of all it will lose the support for dual x8 slots that the P45 chipset will offer, but this is only an issue if you're considering adding a pair of graphics cards to your system.
However, it appears as if the P45 chipset will be DDR3 only while the P43 remains compatible with both DDR2 and DDR3. While the P45 chipset offers official support for DDR3 memory up to 1,333MHz, the P43 chipset stops at 1,066MHz.
The P43 will of course be a fair bit cheaper than the P45.