Just did this a little before Christmas and I used a 1TB Samsung HD103SJ Spinpoint F3. Available for about £40 from most places. I've not had one problem with it since installing it and its very quiet.
It took a lot of reading to find one that people actually said would work and was still available. Most other Samsung drives don't work in it. I did have list of about 6 drives but can't remember where I found it.
Would you think the replacement is straightforward enough? I have experience with installing hard drives in Dekstop PC's and laptops, and in USB enclosures. Is it similar to this?