The question is a bit overly broad. Affiliate links have never gotten a straight answer. The best guidance I've seen is that if you have a completely legitimate product review, then an affiliate link is acceptable (but no one will guarantee that you won't be banned). Mediocre reviews, such as slideshows, are likely to be banned if reviewed.
Now, if we're talking about regular links to websites, then have at it so long as it's a legitimate site- no shortner needed. Obviously, no malware, viruses, etc.