Alright, time to do some maths, which will contain a few assumptions. This is solely on Goku (with exception to 100% FP Frieza, his assumed power level when 'enhanced' and an estimate of Trunks' power level).
The following are the amplifications of Goku's power level in his base form:
Great Ape - 10x
SSJ - 50x
FPSSJ - 75x (probably wrong)
SSJ2 - 175x (as above)
SSJ3 - 400x (as above)
SSJ Great Ape - 500x
SSJ4 - 1250x
Theoretical SSJ5 - 3000x (just to see how big of a number after my calculations would be. I'm not saying he achieved this form, but by assuming he had access to it at the very end of GT)
Ok, now to list the power levels that we DO know:
Start of DB: 10
22nd Budokai (i think): 180
Fight with Raditz: 416
Fight with Nappa and Vegeta: 8,000 (32,000 with 4x Kaioken)
Fight with Ginyu Force: 90,000 (180,000 with 2x Kaioken)
Fight with Frieza: 3,000,000 (150,000,000 SSJ)
With the following calculations, I have based my assumptions on Goku telling Gohan (when he came back from otherworld (not sure if it were in the manga)) he thought Gohan would be twice as strong as when he fought cell, again assuming he trained for the full 7 years. Thus, 7 years of training = 2x previous power level at base. This is most likely wrong, but I to try to calculate the power levels after the Frieza Saga, however massive they are. I also assumed that Mecha-Frieza is more powerful than 100% Final Form, but less than or equal to SSJ Goku on Namek. So for argument's sake, I'll assume the extreme. Then, I assumed Trunks' base power level to be 6,500,000, which means 325,000,000 in SSJ. This could make sense given Vegeta's reaction to the possibility of Trunks being Goku (again, I am referring to the anime here, so I am unsure whether his reaction in the manga was the same or similar, or no reaction at all). Now to calculate:
Return to Earth
9,000,000 base (could make sense given recovery from his battle with Frieza)
450,000,000 SSJ
After 3 Years of training (1.4375x base from above)
12,937,500 base
646,875,000 SSJ
After 1 year in the ROSAT (1,145x base from above)
14,824,218.75 base
741,210,937.5 SSJ
1,111,816,406.25 FPSSJ
The above does not make sense, given he powered up in front of Korin.
After 7 years training
29,648,437.5 base
1,482,421,875 SSJ
5,188,476,562.5 SSJ2
11,859,375,000 SSJ3
Start of GT
11,859,375,000 base
592,968,750,000 SSJ
2,075,390,625,000 SSJ2
4,743,750,000,000 SSJ3
5,929,687,500,000 SSJ Great Ape
14,824,218,750,000 SSJ4
End of GT (~100 years training)
338,703,750,000 base
16,935,187,500,000 SSJ
59,273,156,250,000 SSJ2
135,481,500,000,000 SSJ3
423,379,687,500,000 SSJ4
1,016,111,250,000,000 SSJ5 (theoretical)
I predict the power levels to be far greater than what I've calculated, based on assumptions. However, comparing the 1 quadrillion power level to his 10 when he first appeared pretty much implies he has no limit in power.