Last year alone I went through 4 External Hard Drives and this year have already bought another one, so I have a little experience in choosing which brands to go for.
I started off with a Western Digital Passport (320GB, $80). This hard drive is extremely fast and very light. However, it is very easy to break and if you use it often and travel with it it tends to not last. This type is cheap though, and although larger than the space you want, is well worth the money if you don't plan to travel excessively with it.
When it broke I purchased a Western Digital MyBook, which is much larger and requires a power cord, so probably not what you want. However, I would most certainly recommend one if you do plan in the future to invest in long-term data storage.
I also purchased a 300GB Seagate hard drive for the family to use as a backup source. This had 2 USB cords however, so it is very inconvenient to use. However, it was quite cheap but isn't as fast as the Western Digitals.
This year I bought a Samsung 2TB Hard Drive (which of course has a power cord). The thing to keep in mind with this though is that the Samsung Hard Drive is quite light for its size and is also quite fast (it only cost $100!). I would definitely recommend a Samsung Hard Drive!
In summary, I would suggest looking at the Western Digital or Samsung range of External Hard Drives. They usually have the cheapest prices and run very fast.