What would be your favorite buss compressor plug-in to use on the whole drum kit buss?
I want it to add slap and level it out a little.
The slap is most important.
I have had good success with an LA-2A emulation from IK but there is a narrow volume range where it works. As soon as you start hitting it too hard it looses the magic and gets over-squashed. Maybe try some slight clipping before the LA-2A to keep it in the magic zone? 
 
Post your favorite "slap" drum buss compressor.

I WOULD suggest the WAVES c4 multiband comp.

That's an interesting idea. Can you set the attack time in such a way that it emphasizes the transients?
That's what I was referring to as "slap"; the transient leading edges of the drum hit. 

http://www.tokyodawn.net/.r-feedback-compressor-2/

Also Density is a great drum compressor but unfortunately only 32-bit: http://varietyofsound.wordpress.com/downloads/
 

I'm on the brink of buying The Glue and would be interested to hear if anyone has any experience with it on drum busses.

I tried 'The Glue' for a while but did not like it too much in the end. A really good free one is the Tokyo Dawn Labs Compressor.
 
http://www.tokyodawn.net/tdr-feedback-compressor-2/
 
A nice transparent design. Can get nice sounding drum buses.
 
I like modern sounding compressors on drums. Keep the transients crisp and clean. Don't soften things too much with vintage sounding comopressors. That is how I see it.
 
 

Jeff Evans
I tried 'The Glue' for a while but did not like it too much in the end. A really good free one is the Tokyo Dawn Labs Compressor.
 
http://www.tokyodawn.net/tdr-feedback-compressor-2/
 
A nice transparent design. Can get nice sounding drum buses.
 
I like modern sounding compressors on drums. Keep the transients crisp and clean. Don't soften things too much with vintage sounding comopressors. That is how I see it.
 
 

I beat ya too it! ;)

...but I'm the one that told Jeff about it!!! (the original TDR feedback comp is very good too.)
 
For drums I would think Klanghelm's DC8C2 http://www.klanghelm.com/DC8C.php would do a nice job. It has a punch and snap setting the OP may like.

I like the Waves C4 multiband compressor on the tracks (bass drum and snare in particular) if necessary.
 
The compressor I love on the drum buss is the PSP Old Timer.
 
http://www.pspaudioware.com/plugins/dynamic_processors/psp_oldtimerme/