Surely it's a tarantula. To me (with my rather limited knowledge on the subject) it looks like an Avicularia... However, I seriously doubt that *anybody* could id it to exact species on basis of that photo alone. Was it seen in Guyana? Also remember, that all the time new tarantula species are being discovered... we are talking several new species a year. Especially in South America. Last number I heard was something like 900+ species worldwide... surely it has crossed a thousand by now...
In Ecuador I spoke to a colletor who also had a ph.d. in these "small cuties"... He had been in Ecuador for five weeks when I met him, and in that time discovered what was apparently two new species... he even seemed quite confident that he would discover even more newbies on that trip!!!
...And by the way Jacamar; if you'd like to see more of these nice little fellows, find the nearest woodland (or preferably forest) in Guyana. Then look into all the small holes and crevices you can find with flashlight (obviosly you shouldn't use your fingers to check!), and, after a fairly limited time you will see a pair of small eyes glowing back at you, and usually also the front legs. Voila! You have found your first tarantula. Of course I wouldn't recommend you trying to get it out in any way... you will almost certainly hurt the tarantula in the process, and if unlucky yourself to!
Being somewhat of a naturefreak I looked down into small holes and crevices all the time in various countries I visited in South America, and quickly noticed, that these generally peacefull animals are quite common... If visiting a lodge in the Amazonian rainforest the likelyhood is, that there will be several living within just a few 10's of meters from your lodge. The likelyhood even is (that is what I found on numerous visits), that there will be a few living below the lodge! Of course once again, they are generally peacefull and harmless creatures.
- And a last note: You write "have never seen one of these alive, I only see them after they are caught." Well, the somewhat terrifying thing is, that they are still alive at that point. The female wasp has just paralized it. Then she carries it into a pre-made burrow, lays a single (sometimes more) egg. After a short time the egg will hatch, and the larvae will eath its way through the paralyzed but still alive tarantula! How is that for a terrible death!
Rasmus