I own a DSO-2250, 8 bit 250 Msps USB DSO. It uses the PC's screen, which is fine for me. It's very handy and cost ~$300 inc shipping. Unfortunately the software that comes with it is not the best and there is a large amount of background noise in the hardware.
Rigol is quite alright & can be cheap - a colleague had a one, something like 50Msps and upgraded the firmware to allow 100Msps (both the 50/100 MHz versions use the same ADCs, just the extra performance is locked out on the check model). NOTE: I'm not actually sure about the sample rate of his DSO, it might be different.
The main problem with the both of the above units is the sample rate is reduced depending on the zoom level - so you cant zoom in on a stored screen very far at all. Also, the rigol apparently suffered badly from aliasing.
Sorry, that's just off the top of my head - which is not functioning well at the moment... so take with a grain of salt & make sure you research any suggestions people give you.