I have found this site http://www.worldtravelguide.net/country/</a> quite useful. Pick the (continent, then) country you need the info for, choose "Passport/Visa" from the menu on the right, and there you go- useful information for British, Australian, Canadian, USA, and Other-EU citizens.
This site also has some information about whether return tickets are necessary.
Hope this helps!


I checked a few of the visa info listings (Singapore, Egypt, UAE, etc) on the site mentioned in titaniumalison's post; in every case they were wrong. I would definitely NOT recommend relying on the information presented there.
Instead, I recommend using the database that the airlines use at check-in time to determine your eligibility to enter; the information is collected directly from the governments in question and updated immediately. It includes pretty much all destinations and passport nationalities:
IATA passport/visa database

wow rajulkabir- eep. I checked the South American ones, seemed to be mostly correct. Oh well, I recommend checking both- my link is handy for seeing if you might need to think about onward tickets.
titaniumalison

Still leaves me with the problem of different requirements for overland travel but thanks anyway.

The IATA database also discusses onward ticket requirements.
Nothing personal, but I really wouldn't mess around with getting critical information like this from a web site like worldtravelguide's that is so thoroughly inaccurate. It adds nothing useful and only increases the chance of a ruined trip.
Scott: Overland entries are normally more casual than air arrivals. I cannot think of any time when I have been asked to show onward air tickets or anything. There are a few countries where foreigners can only enter at a subset of the border posts, but this tends to be poorly documented online. Sometimes these limitations only apply to travelers without a visa. If you are entering a developing country by land it is best to speak with the staff of one of that country's consulates, or post on Lonely Planet to get first-hand experiences. The Lonely Planet guide is usually reasonably accurate in these matters, if a little conservative at times.