Which memory should I get?

Those are all very good and you will not be able to tell the difference between them performance-wise.

So far, I'm going to go with the second choice. I also found these:

http://www.newegg.com/Product/Prod [...] PR800C44GK

which I can get for about $55.

Well i have 4x1GB OCZ REAPER(Not HPC model) DDR2 800 RAMs with 4-4-4-15 timings and i'm happy with its performance,but the Flex model has slightly better timings (4-4-3-15 vs 4-4-4-15)so i say go for the flex model it has better timings and its cheaper too

Well in real time benchmarks,u really won't find a noticeable difference between DDR2 1066 and 800,but because the DDR2 800 models u posted have lower timings(which is better for OC'ng)i recommended going for them.
Don't get me wrong i am not saying DDR2 1066 is bad,I'm saying that because the difference between 1066 and 800 isn't much then go for the model which has lower timings

try crucials ballistix series. bit expensive, but real perfromance.

I asked to see other people's recommendations. Those are cheap and got good ratings. Thanks for your help.