I've got 2 wacom tablets here, both are actually so old they're serial devices not USB (ArtZ II 9x12 & 12x12 from the 90's) but both still work fine so I've never had cause to replace them. I've used several different applications with them over the years too, but I've not ever gotten to the point where I feel they're a necessity as it's yet another device to remember to configure.
Assuming that you're on windows:
Tablet2midi was the best of the lot for me. Set your wacom to scale the screen to fit the surface so that it fills the full thing and you can print out maps that will correspond to input properly. I actually prefer aspect scaling (keeping the screen's aspect ratio) myself since my widescreen throws me off when using the 12x12 wacom without the aspect scaling, so I modify my tablet2midi 'map' (printed paper inserted into the wacom's underlay) in illustrator (print2pdf or adobe's pdf print driver etc) to fit. The only downside for me was being careful about when I land the pen to avoid parameter jumps while a voice was playing on something.
Wmidi was moderately interesting as an 'experimental' way of generating note sequences, but wasn't my preferred tool for the tablets.
Most of the OSX apps I've used over the years that are actual wacom/tablet midi apps (versus a generic input app to convert to midi) have disappeared, the only one I can still find is
http://www.musicunfolding.com/MU_MIDI_Controller.html which is closest to wmidi.
PD, MaxMSP & Supercollider all have native support for tablets, and linux has a HUGE array of open source tools for grabbing tablet input and doing whatever you want with it. It's been 4-5 years since I fiddled with that in linux though so I'll refrain from posting as I'm sure the landscape has totally changed.