Just to put it in pesspective, lets look at the paladin abilities and see hwo they help him do his thing.
1) Detect Evil. Find the enemy, kill the enemy. Doesn't help in combat, but at will abilities are always good.
2) Smite Evil. Gives the paladin better hit and tons more damage against evil creatures. Once the paladin gets a few of these under his belt (through levels or feats) he can rack up a lot of damage agaisnt evil.
3) Divine Grace. This one really depends on the paladin. It can make the paladin's saves better than a monks, comparable, or not really much of a help at all depending on the paladin's cha.
4) Lay on Hands. Healing is always always good. For a front line fighter, being able to heal yourself is great.
5) Aura of Courage. We all know fighters have crappy will saves. This helps compensates partly for the fighters innate weakness. Paladins can stand against scary stuff and not worry about their will saves hindering them. Combined with their divine grace, they handle will saves pretty well..
6) Divine Health. Immunity to most diseases doesn't help in combat that often, although diseases could be a problem for the party at low levels when you first get it. However, immunity to magical diseases is nice. Trust me, you don't want mummy rot.
7) The mount. Some hate the mount, every paladin I've seen played loves the mount. The mount is a whole additional combat power. It can attack, it increases your mobiility, it can have a decent AC with mounted combat. I've seen paladin mounts be a major force in combat.
8) Remove Disease....alright, this one just blows
9) Turn Undead. Not that strong for a paladin, helps turn the crappy undead, allowing the paladin to focus on the big wigs. Can also be used to power divine feats, which are very powerful in general.
10) Spells. Let's take a brief look at some of the paladin spells. 1st of, paladins can heal more with their spells AND can use healing wands (very important). They get bless weapon, autocriting against evil is nice. Protection from evil is never bad, especially at low levels. Divine Favor can become very nice at high levels, not really great when the paladin first gets it. Bless can be a nice party buff if your facing something really nasty. At 2nd level, resist energy can be a big blessing. I don't think the paladin's 3rd level spells help that much in general, but his 4th level dispel evil, holy sword, and DEATH WARD!! are great spells to have.
So if you compare this list to the monks, you can see that the paladin's ability are very focused towards protecting the paladin and helping him kill evil. Thing is, in most campaigns the party is fighting evil all the time, so these abilities get used a lot.
The monks abilities are scattered more, and don't have the same focus. Also, its main focus, anti-spellcaster, is a lot rarer than anti-evil.