Most places can ship just fine if the weather is above 20F, so you should be OK. A lot of places don't like shipping if it's above 80 or 90F.
I've had great experiences with The Wet Spot out of Portland, OR. That's a pretty long way from Pittsburgh, but IME they're the best. Their selection is amazing, especially if you're looking for obscure fish to fill in a weird biotope. They also quarantine all their fish, so they don't bring in sickness and almost always arrive healthy.
I've had mixed results with Aquahuna. Their prices are very good, as is their shipping fee. They have a very generous policy of refunding or replacing fish that die within three days of arrival. On the other hand, they don't do next day shipping, so if you're outside the Pacific Northwest, expect some DOAs and sick fish. Out of 16 danios and 8 hillstream loaches in my last order, only four danios and one loach made it long term, and they introduced ich into my 150g. BUT...if you're willing to quarantine properly, they are a very affordable way to stock a tank.
For bettas and inverts, I've actually had really good luck with Ebay. Order only from well established sellers with at least 98% positive ratings, and quarantine.