This being the case, I decided to begin a thread listing in-game houses that are good to use. I am sure I've seen people discussing the subject in another thread some time back, but I searched back 9 pages and couldn't find it. If anyone knows where it is perhaps it could be added here?
To begin I'll mention a few places I know of, some involve quests but I won't actually mention them here so as to avoid spoilers as much as possible. You can, of course, just kill the occupants of any place that strikes your fancy, but I don't usually attack NPCs unless provoked. So, anything I mention here (with one notable quasi-exception) is either non-violent or there is an actual quest in which the owner is "removed." :
Seyda Neen
*Vodunius Nuccius' cottage
*Foryn Gilnith’s Shack
Balmora
*Dura gra-Bol's House
*Ralen Hlaalu's Manor
Ascadian Isles
*Dren Plantation (only a good idea at higher levels
Also a good bet are miscellaneous Velothi towers; they tend to be occupied by Telvanni mages who will usually (unless you are a member of House Telvanni) attack you on sight, thus conveniently "vacating" the premises. The drawback, of course, is that the old Velothi towers are rather remote.