Depends on your needs and budget.
As others have mentioned Bitscope http://bitscope.com/
is cool. Its way cooler because the software can run on Linux!
There are others out there, like this one, http://microcontrollershop.com/product_info.php?products_id=1426
Both do realtime display of data and can save to file for later analysis. Both have high frequency >= 50MHz support.
Am still checking my resources if I should also get one
I have a logic analyzer, my gripe is that it can display realtime data from the device under test, that's where the DSO comes in. The logic analyzer has decodings for common protocols, I2C, serial, SPI. Makes life easier.