A Picasso4 is a great Z2/Z3 card. It has modules for TV output, TV input and Sound. It includes a programmable flicker fixer that allows you to watch OCS/ECS/AGA modes at 100Hz for example. Super-HiRes is not displayed correctly (but it's useable).
If you can't get a Picasso4 another common and very nice card is a Cybervision64/3D. It's a Virge with 4MB and Z2/Z3. Its bus is slower and doesn't have integrated scandoubler, it's optional and it's not 24bit (so colours won't look as good as with a real one)
Another very nice Z3 card is the Cybervision64 (without the "3D" suffix). It's zorro3 only and its bus is very fast. Its blitter (a Trio64) is slower than a Virge, but it's quite good.
With ZorroIII you can also plug in a PCI busboard like Prometheus (it's a Zorro3<->PCI bridge). In that case you can put a Voodoo3 to your miggy, but you'll lose autoswitch and scandoubler/flickerfixer
With PPC cards you can also use BlizzardVisionPPC/CyberVisionPPC, Permedia2 based cards with 8MB, these are very fast and nice but you need a ppc card (the connector is a custom one).
A RetinaZ3 is OK. A RetinaZ2 is rubbish because it doesn't support Cybergraphics/Picasso96 so DO NOT BUY ONE.
The rest of the cards (PicassoII, GVP Spectrum) are slow for my taste. Most of Z2-only cards have slow blitters and you will have to use 60Hz screenmodes at 800x600 when you want to use 16 or 24 bits, but anyway these are "slow" cards (but miles better than plain AGA if you plan to use WB)
