PrimeGrid has a challenge on right now for PSP/SOB Sieving, they are easy lightweight (short) tasks. Initial one time only download is approx 10MB.

Aqua and QuantumFire are both rewarding with big points for CPU users.

Naturally the GPU projects reward well too: Collatz, MilkyWay, PrimeGrid AP26 and Seti & SetiBeta when they are on-line.