Pretty much anything from a known manufacturer such as Iomega, Seagate, Western Digital. You can get cheaper - but when you're relying on it, it doesn't make sense to scrimp. As it's a laptop, portability will be important so you may want to find one that's powered from the USB port - although I think those are typically only for smaller size drives. If your laptop supports USB 3.0, look for that in a drive - data transfer will be much faster.
If you can afford it, btw, get two - and back up one to the other every so oftem if what you're storing is important to you.