From NDCA Tempi for Professional and Amateur competition
Measures per minute
INTERNATIONAL
Standard
WALTZ 28
TANGO 32
VIENNESE 56-58
FOXTROT 28
QUICKSTEP 50-52
LATIN
CHA CHA 31
SAMBA 50
RUMBA 26
PASO DOBLE 60-62
JIVE 44

AMERICAN
SMOOTH
FOXTROT 30
WALTZ 28-30
TANGO 30
PEABODY 60-62
VIENNESE 54

RHYTHM
BOLERO 24
CHA CHA 30
MAMBO 47
MERENGUE 29-32
PASO DOBLE 58-60
RUMBA 32
SAMBA 52
SWING 36
WC SWING 28-32
POLKA 60-62
HUSTLE 28-30

The international ballrom tempi are:
Slow waltz: 30 bars per minute (between 28 and 30 is used in comps)
Foxtrot: 30 bars per minute (again 27 - 30 is used in comps)
Tango:

Obviously that depends on the dance. Different dances are done to different tempo music. And even if there is a sort of standard tempo for a given dance, there's always a range that goes from somewhat slower to somewhat faster than the standard that's still acceptable. If you want an idea of what tempi are used in competitions, you can try looking in the rule books of dance organizations for that information. I'm almost certain that USABDA still puts their rule books on line, so you could check their web site for one. (It's probably usabda.org, but search for USABDA in Google or something to make sure; the official site has to be high up in the hit list or something's wrong.)

--
James Marshall
marshall@astro.umd.edu
http://www.astro.umd.edu/~marshall

my previous post was unfinished - i hit the wrong key!
Tango is 32 /33 bars per minute
Quickstep 50 BPM and viennese waltz 60 BPM

The character of the tune/song is very important too - to match the nature of the dance. Some slow waltz tunes (as an example) seem much more enjoyable to dance to than others.
Foxtrot is meant to be a smooth flowing dance, so jerky syncopation in the music is hard to interpret well.
Of course, personal taste counts too and there's "nowt queerer than folk" as they say in the north of england