When you do not know someone that well, it's very hard to buy them a gift. Normally a gift is purchased based on context. You know something about the person and can buy them something they like. When you do not know someone that well, you need to get more of a generic gift. Learn some ideas that you could use if buying a gift for someone you do not know well.
Gift cards to popular stores are a great idea. You need to buy them from places that you know are all over the country so that they can be used. The two most popular to get are ones to electronics stores or clothing stores as these are things people buy all the time.
You can also purchase restaurant gift cards for people too. Find ones that have more than a few options on them. Someone might not like the Italian place on the card but could like the seafood option on it.
Find a popular and useful TV gadget as a gift. Many of these are very cheap in the $ 20 range and are useful. Quite a few offer you a free shipping with when purchasing. You can get two cheap gifts this way or keep one for yourself and give the second free one away.
A one year magazine subscription is a good gift idea. This is best if you know their favorite hobby.
Make a charity donation in their name. Not everyone likes this, but it's a touching gift for many to see that money was given in their name to a charity organization.
Buy a generic but useful item that someone might use. This can be something very simple like a picture frame. Since it's generic, it's more likely the person will like it.
Instead of cash, you can buy something like a Visa gift card. These can be used like a credit card and look a bit more thoughtful than just cash.