Since discovering tank tops w/ the built in shelf bra, they are my new favorite clothing item. They are not actually "sports bras" but they are great for working out and lounging around. It almost has the feel of no bra, but it looks like you're wearing one. I even sleep in them very often. I am not very busty (34B) so they work great for me. They probably wouldn't offer the best support for larger busted women. I usually get mine at Old Navy. Just a suggestion.
You can do either. I usually get mine at the store. They had some online yesterday that had the racerback on sale for around $8.50 I believe. Go ahead and get yourself 3 or 4 because you are going to love them!!!
Title 9 Sports online has many long sports bras. I have never bought one, since I have tiny t!tty-scraps and flat ripped abs I want everyone in the world to admire , but I have looked at them for years in that catalog.
Actually, I don't buy them because they are more expensive than the short ones.