Spotting

Yes, Guanyang, Exophthalmus jekelianus is quite a close match. The scientific ID that I suggest would be Exophthalmus cf. jekelianus, since these Entiminae are really tricky. As you already mentioned there are many similar looking weevils around. With the cf. we are on the safe side :-)...
Good job!
http://natgeo.nikkeibp.co.jp/nng/article...
http://www.inotaxa.org/jsp/display.jsp?c...

Most probably Exophthalmus jekelianus (Entiminae, Curculionidae). There are several species with very similar color profiles.

Based on this, https://www.flickr.com/photos/andresmoli...
it's a Short-snout weevil (Compsus sp.) They seem to be pretty common on citrus farms in northern Costa Rica from what I've seen.

Curculionidae.... still looking. found another one a couple of nights ago, though much smaller and pale green.

I would keep the names empty, so it remains "unknown". If soembody passes by, he will find it for an ID. But I would mentioned the following in the description section, so it will be shown in the search engines:
"Curculionidae, Weevil, could be Entiminae".

Okay, it looks like we've found this guy (Bayucca's flickr link) but I'm not sure ... should I just say "weevil"?

Thanks, that second one is it for sure. Buenas noches to you... in a few hours.

Curculionidae, most probably Entiminae.
Same like this:
http://www.botany.hawaii.edu/faculty/cw_...
http://www.flickr.com/photos/27423590@N0...
Reminds me somehow of Compsus sp., but only deep in a hidden place in my empty and tired brain. Buenas noches!