Click on any of the border images to see what it looks like in-game.
(last updated: April 21, 2013)

160x144 (standard) borders – should work well for any game.
160x144 black border
is built into Goomba
Borders that extend to the right, but not the left (because Mario cannot go backwards.)
Super Mario Land draws enemies farther outside the 160x144 area than most games do.
Borders that extend to both the left and right.
If you use these, remember that Mario can't go further left than the original screen size.
Want a little color? Here are versions of the above borders with a color HUD overlay.

Some nice color palettes:

[Super Mario Land #1]
bgr=#FFFFFF #AAAAAA #555555 #000000
win=#FFFFFF #AAAAAA #555555 #000000
ob1=#FFFFFF #FFD090 #C00000 #800000
ob2=#FFFFFF #FFD090 #C00000 #800000
[Super Mario Land #2]
bgr=#FFFFFF #CAAA8A #866646 #000000
win=#FFFFFF #CAAA8A #866646 #000000
ob1=#FFFFFF #FFD090 #C00000 #800000
ob2=#FFFFFF #FFD090 #C00000 #800000
[Super Mario Land GBC]
bgr=#B5B5FF #FFFF94 #AD5A42 #000000
win=#B5B5FF #FFFF94 #AD5A42 #000000
ob1=#FFFFFF #FF8484 #943A3A #000000
ob2=#FFFFFF #FF8484 #943A3A #000000
This palette comes from the PH boards.