Invader 2

Highly recommended. The sequencer recording function is fun to play with, I'm just purchased the plugin and it sounds great, easy to use, clean UI. I feel bad I couldn't donate more than $7. This is a $50 plugin IMO. Good for way more than just bass - it comes with a nice set of presets to show what all it's capable of (which is basically anything from bass, to pads, to keys, etc.). I particularly like the bells with the ARP. You can get some great sounds on the lower end of things especially. Download the demo and get to know it, then buy.