I used a stock AM2 heatsink for like 2 weeks when I ordered my OEM X2 240. They WILL work, but I wouldn't suggest it as a long term solution. Even a $20 Aftermarket HSF will do a better job than a Stock HSF.
AM2/AM2+/AM3 motherboards are all within the AM2 designation as far as HSF mounting and design go. This isn't a question of stock vs aftermarket. AM2 is physical design. AM2/AM2+/AM3 are the chipset and CPU specifications.
Yes, any HSF that is designed to work with AM2 will work with all the above. If AM3+ or whatever they call it will be physically different than AM2, then it will require specific hardware, but if it is physically identical, then it to will take an AM2 designated HSF.
I have built a few AM3 PCs in the past few months (including my own) and can say from personal experience that they are no different in physical design from the previous generations, and utilize AM2 heatsinks, stock or aftermarket, perfectly fine.