Hi immi, and sorry it took so long to reply. The difficulty is that there is no single answer to this, as it depends mostly on the existing design of the website.

If the login is available on every page, best not include all the options everywhere - just the login link and an options link to a dedicated login page with all the lost password and other rarely-used options.

My personal preference is to incorporate a login dialog on the page rather than just a link to a login page.

According to SURL (Optimal Web Design [psychology.wichita.edu]) the best place is the top left corner:

The login/register button was expected to be located at the upper-left corner of a web page (Figure 6).

HTH

I'd say most that try this are - upper right. So . .

Others just bring up a separate login page.

I generally use top-right or bottom-left ...

I have never had to include a login but if I am looking for one I first look top right and secondly to the left underneath the site logo. After than the back button starts to look attractive.

It also depends on how much of the content is viewable without login. Adwords/Adsense has a huge @ss login because there's not much to do if you don't log in. Google Homepage has a small link on top right. I think that's a pretty good general guide although each site is different and user testing helps the most.