I've just started to play Nethack (games you can play in a shell are useful). What is the easiest role and race to start with?
How easy any given class is depends on your playing style of course, but most people agree that valkyrie is the easiest class in nethack. They're good for fighting, they start with good equipment (+3 small shield means that once you've picked up some body armor, you'll have a very nice AC for a starting character) and food and they have a decent quest artifact. They also get speed at level 7.
Race doesn't matter as much, but dwarves are a good choice for valkyries, because they have good stats for fighting and most inhabitants of the gnomish mines will be peaceful towards you (so you can go shopping without endangering your life - as much).
Not to diminish the answers already given, but a "beginner" should definitely choose a random role and race sometimes (often IMHO) to experience the many and varied styles and issues facing a NetHack player.
Yes, at some point specialise if you prefer, but trying all roles and races is definitely worth while.
Chaotic Orcish Barbarians have high hit points and start with poison resistance. Because they are Chaotic, you can kill peaceful townspeople if you want to. The Valkyrie is probably slightly easier though.
Lawful Dwarf Valkyrie would be my suggestion. Lawful means you #dip for Excalibur, and being a Dwarf greatly decreases the number of aggressive mobs in the mines.