dlesaux
Plugin Alliance just came out with a free bass enhancer plugin called bx_subfilter. It's basically a resonant filter optimized for bass frequencies. Try it! It may be what you're looking for!

scook

Sanderxpander
It's much pricier than the Waves ones (on sale) though.

Melda plug-ins go on sale for 50% off regularly, are true VST2 and VST3 plug-ins, have free updates for life, no WUP and simple serial number protection.

Kamikaze

dlesaux
Plugin Alliance just came out with a free bass enhancer plugin called bx_subfilter. It's basically a resonant filter optimized for bass frequencies. Try it! It may be what you're looking for!

This seems similar to Bark of the Dog, with a little more control

Sanderxpander
I see some good advice on bass processing here by the way, but for those who don't know exactly what MaxxBass does - it separates the audio into highs and lows with an adjustable crossover point. Then, for every fundamental it finds in the lows, it generates upper harmonics. You can then use sliders to blend the original fundamental and the generated harmonics. You could even lower the level of the fundamental and there will be a psychoacoustic effect of it being there. The main purpose of this is to let deep bass translate better to smaller speakers, although of course the creative sky is the limit.