Yes, 8GB will be enough currently. However, if you are building a new PC, you will better off spending a little more and just getting 16GB now (2x8GB). There are two reasons for this:
1) Memory these days on newer chipsets are only guaranteed to work in kits together (2x4GB, 4x4GB, 2x16GB, etc.). If you buy 2x4GB now and then next year buy another 2x4GB kit, there's no guarantee that other 8GB will work, even if the same exact model. This is because memory sold in kits are guaranteed to work together and tested. Manufacturing variances in silicon at the microscopic level in different yields can cause problems. Kit form modules are cut from the same silicon wafer.
2) Memory prices are volatile and can rapidly rise in price if there's a supply disruption due to external reasons (natural disaster, factory fire, etc.). While memory prices are stable right now, there is no guarantee they'll be the same next year. They certainly won't go down (and older ram like DDR3 and DDR2 actually goes up in cost over time as new supply diminishes).
Regarding general memory requirements, every 2-3 years it doubles. Eight years ago 2GB was the upper norm. Five years ago 4GB was the upper norm. Two years ago 8GB was the upper norm. Next year 16 GB will be the upper norm.