[Build Help] How much memory should I get on SSD?

What's a good solid number?

SSD's I was looking at:

http://www.newegg.com/Internal-SSD/BrandSubCat/ID-1455-636

http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&N=-1&isNodeId=1&Description=sandisk+extreme+ssd

EDIT: So the consensus is that I should just get an HDD?