AGP:
As far as I'm aware, the only AGP card available from ATi is the mobility 9600/9700, both of which have been a massive success for ATi. The mobility 9600 is a mobile version of the desktop Radeon 9600, the mobility 9700 is a mobile version of the 9600XT *not* the desktop 9700 as the name suggests. The 9600/9700 both offer full DX9 support, and offer smooth gaming at around 1024x768 with details set between medium and high. As games get tougher these cards are starting to show their age but they remain a good choice as generally they are the only card available in this range
PCI-Express:
X300/X600 - Now the confusion begins...both these cards are basically mobility 9700s using PCI Express instead of AGP, the X300 uses a cheaper, less mature manufacturing process which means it is clocked lower than the X300, hence the performance is less. There are a couple of versions to look out for, the X300SE is an X300 with the memory bandwidth reduced by half, substantially reducing the performance, people often think the 'SE' means something better, but sadly not in this case. I don't think they are available in notebook form yet, but probably will in time, that is X300s using 'hypermemory' - a small amount of memory onboard the graphics card and then using system ram to make up for the rest. The X600 offers similar performance to the mobility 9700, assuming both are clocked at similar speeds.
X700 - this is ATi's new midrange graphics card with eight rendering pipelines and 128bit memory, it offers similar performance to the former highend ATi cards such as the 9700 and 9800 pro. Availability of this card still seems relatively limited unfortunately, it gives good performance without forcing the laptop into the desktop replacement category for size and weight
X800 - this is a slightly lower clocked version of the desktop X800 pro, with 12 pipelines and 256 bit memory, it's currently available in Clevo based machines such as the Rock Xtreme Ti and the Xtreme XT. It is an incredibly fast mobile graphics card, outperforming nvidia's standard 6800.
X800XT

E: ATi now have a full 16 pipeline mobile part, offering similar performance to the 6800 Ultra but has now been surpassed by the Nvidia 7800Go