also, I would be interested in hearing about people's favorite external hard drives and brands
You can't say generally, that one company is better or not, every company has had drives that failed, some just get more publicised.
(Samsung had with F3 Drives, Hitachi had, when they took over IBM and purchased their production left overs and sold them as Deskstar-Series. Hitachi Deskstars with model numbers starting with IC35... were IBM, Deskstar with HDS72... were Hitachi and did not fail so often, but this was long time ago. WD had in the beginning of introducing their Caviar Green series. Seagate was always said to be failing a lot, but you can't say how it is with latest versions.)
Manufacturers also update the firmware of their drives resulting in speed differences and reliability.
When you look at xlr8yourmac.com it seems Hitachi and WD do make the fewest failing drives (or not properly compatible) with Macs. But you can never say, whether this is a picture you get, because not all people complain publicly.
Two things to consider though!
1. Basically I think every drive will do its job. There are some optimized for AV (audio-video, mostly home electronic appliances like HD-Recorders). But xbitlabs discovered that one generation (it might has changed now) of the WD AV-GP Series is not doing every media job really good. read more here
http://www.xbitlabs.com/articles/storage/display/15-2tb-hdd-roundup.html (but do not apply these results to Macs and the latest HDD models out).
2. I would rather by an external enclosure and HDD seperatly, because most enclosures do have Seagate HDDs, if it is not an enclosure from a HDD manufacturer itself
and most external HDDs will have 5400rpm drives
(I once asked Hitachi to tell me which drive enclosure comes with which HDD type and they said they do not know because they use several models in different enclosures)
If you need the speed of 7200rpm drives, be aware of 5400rpm drives (whether one needs 7200rpm for an external HDD or DV-data is another question, but you might want to later use it as an internal HDD and then you might prefer 7200rpm).
PS: if you or she is very anxoius of data loss, you can minimize your risk by taking two 1TB instead of one 2TB. If one of the 1TB crashes, you still have the data on the other, while on the 2TB all data will be unaccessable perhaps. But this is for anxoius people only (for cost critic environments one would do a backup of critical data anyways, right?).
PS2: for your boot drive: consider SSD speed vs high price, low reliablility (lower lifetime), low write speeds (high read speeds though).