These days there a many good inexpensive HD cameras. I like the Canon Vixia/Legria series. The best output is HDMI. That would mean you'd want either a Matrox MXO2Mini which works with desktop PCIe or laptop with Express port or, soon, all Thunderbolt MacBookPros, or you could use Blackmagic Intensity Pro for desktop PCIe.
As to "just plug in" unfortunately firewire DV cameras, while still available, are on the decline so I would not recommend them. USB is pretty much limited to webcams. There are very very very few video cameras with live USB out and most of them are poor quality compared to HDMI out cameras.