Khan Academy has some bells and whistles. The drawback is that it requires a lot more practice to go up the ladder than Aleks.
We do Aleks and supplement with Khan when my son needs more explaining (or rather more patient explaining) than I can do, but having the Khan button in Aleks would be great...
How far ahead is your son at this point? Last year we did Dreambox with mine (also 8/2nd grade this year) and he loved it -- Flash based, game-like, and all instructions verbally given. Lots of virtual manipulatives to get the concepts and number sense down. They have added a 4th grade level a few weeks ago, so you might still be able to benefit from it.
Minuses: little to no actual instruction on concepts (probably slightly worse than Aleks on that front, so keep Khan available), and doesn't cover the full curriculum (up to last year no time, no money, no geometry, although that's changed with the last upgrade). We also had to drill on math facts separately, since after a certain point Dreambox seems to assume them known, and that generated a lot of frustrations. xtramath.org, and that thing where you are a green lizard like monster in the dungeon?
Another free game-like option is MathWizz. It goes higher in grades than Dreambox but felt a bit less polished visually and... harsher, somehow (mom's judgement here, I was looking for something that would also be suitable for then 4yo #2).
