The DS is $130, the PSP is $170 for the stand alone and $200 for the bundle. You can buy a mic for the PSP. As far as I know, the DS online is a bit gimped like the Wii, whereas the PSP's is a wide open system like the 360 or PS3.
Here's other threads with decent info, although they're mostly fanboy banter:
http://www.vgchartz.com/forum/thread.php?id=35549&start=50
http://vgchartz.com/forum/thread.php?start=50&id=34520
My Top 5:
Shadow of the Colossus, Metal Gear Solid 3, Shenmue, Skies of Arcadia, Chrono Trigger
My 2 nex-gen systems: PS3 
and Wii 
Prediction Aug '08: We see the PSP2 released fall '09. Graphically, it's basically the same as the current system. UMD drive ditched and replaced by 4-8gb on board flash memory. Other upgrades: 2nd analog nub, touchscreen, blutooth, motion sensor. Design: Flip-style or slider. Size: Think Iphone. Cost: $199. Will be profitable on day 1.
