The benefit of going with the PS3 is that you do get a BluRay high-def DVD player - you've already 'invested' in the HD TV so if you get the PS3 you'll be able to pick from the small (but growing) selection at your local Xtravision.
The benefit of the PSP is that its cheaper and as a handheld system, you're not going to have to give up your regular television viewing habits to your gaming husband ;-)
For an infrequent gamer, I'd suggest the PSP - but the BluRay player in the PS3 offers you something also. On a put Toys for Boys scale, the PS3 definitely had the edge.