I ravelled through those areas with my rack and rope and was rather dissapointed. The place is great if you want to summit things, but for rock, it's a bit dull. There is stuff if you look hard enough and there are some climbing walls where you'll meet locals who can tell you how to get to the crags. It helps if you speak Spanish. some spots worth looking at are:
Bariloche, Argentina
La Paz Bolivia. There's an area in the southern part of town which has a few bolted routes. Just ask at one of the mountain guiding shops for directions to the climbing at I think either Miraflores or Flores.
Peru. Go to Huaraz even if it's not for climbing. It's a great place and there's a few daggy local crags to check out.
Ecuador. You can track down some good small crags, but there's some hard core stuff on them. There's climbing wall/towers in towns such as Riobamba and Quito.
Check out this thread on rockclimbing.com
Take you harness and shoes and see what happens. But, if you want a good climbing trip, take you trad rack and your tent and head to Bariloche. Although it will soon be covered in snow!