Hans-Georg Michna wrote:
Depending on what your demands of picture quality are, the
choices are these:

Poorest
vvvvvvv
* Cheap consumer zoom with telephoto converter
* Cheap consumer zoom
* Quality zoom with quality telephoto converter, ideally by the
same manufacturer and advertized as matching the lens
* Quality zoom
* Quality zoom with image stabilizer
* Quality fixed lense
* Quality fixed lense with image stabilizer
^^^^
Best

I agree with this assessment. A great starter wildlife
lens that gives great results on Canon DSLRs is the
300 f/4 L IS (about $1100) and add a 1.4x TC (even a Kenko
pro 300). In my opinion, IS makes the difference in
shooting from a safari vehicle, especially near sunrise
and sunset.

My safari images from Tanzania this January:
http://www.clarkvision.com/galleries/gallery.africa

A colleague used a 300 f/4 on a 20D and got great results.
I took a 300 f/4 as my backup lens (I mostly
used a 500 f/4). The guy with the 300 f/4 and a
beanbag got some shots I missed because he could move
and point faster than I could with the 500 mm.

Roger