The MB-33 is a 303 clone in 1U rack format by MAM in Germany.
It has the same control as the original 303, and instead of the sequencer you can control it over midi. Accent is emulated via midi velocity control over 120, and the slide is automatic when you play legato mode.
NEW : They have upgraded the filter to a 18db-TB-303-like.
The low price of the unit is a positive point. There is also a MKII version with additional VCF input for external signals.
In addition of the MB-33, you can also get their SQ-16 step-sequencer if you want to get that TB-303 sequencing feeling added to this unti or any other midi equipment.
You can check the following URL for more infos http://www.mam-germany.de/com/index.html