Android - Free PDF reader for Android phone that has a "Go To page" function

You can goto page in 'fit to screen' or 'continous scroll' mode (but not 'reflow text') by touching at the bottom of the screen and it'll make a scroll bar turn up. As you drag your finger left and right you'll see the page number and total number of pages at the top left of the screen.

Edit in 2015: Slightly different now: touch at the bottom, then you'll see a page number on the right edge of the screen, which you can drag up and down.

Adobe Acrobat Reader has the function, on the right you have a little arrow with the page number, tap on it and you'll be able to enter the page number