OptiFine

By default, Minecraft is limited to rendering blocks at 16 pixels by 16 pixels.

This mod adds support for HD textures; 32, 128, 256, even 512 pixels per block. It also adds a lot of options for better looks and better performance. Doubling your FPS (frames per second) is quite common.

We recommend the OptiFine HD A4 Smooth for Minecraft 1.1

Features
- doubling the FPS is common - decreases lag spikes and smooths gameplay
 * FPS boost (examples)

- HD textures and HD fonts (MCPatcher not needed) - custom terrain and item textures - animated terrain and item textures - custom HD Font character widths - custom colors - custom block color palettes - unlimited texture size
 * Support for HD Textures (info, examples)

- from 1% - smooth lighting without shadows - to 100% - smooth lighting with full shadows
 * Configurable Smooth Lighting (examples)

Synchronizes framerate with monitor refresh rate to remove split frames and smooth gameplay
 * Performance: VSync

- more efficient, less artifacts - Fast - faster, some artifacts still visible - Fancy - slower, avoids visual artifacts
 * Smart Advanced OpenGL

- Fog: Fancy, Fast, OFF - Fog start: Near, Far
 * Fog control

Visual effect which makes distant objects look better by smoothing the texture details - Mipmap level - OFF, 1, 2, 3, Max - Mipmap type - Nearest, Linear Check the OptiFine AA edition for even better texture smoothing with Antialiasing and Anisotropic Filtering.
 * Mipmaps (examples)

Fixes grass blocks side texture to match surrounding grass terrain
 * Better Grass

Fixes transparent blocks textures to match surrounding snow terrain
 * Better Snow (examples, credit)

Clear, transparent water with good visibility underwater
 * Clear Water (examples)

Use random mob textures if available in the texture pack
 * Random Mobs

Increases view distance 3x.
 * Far View

- Smooth FPS - stabilizes FPS by flushing the graphics driver buffers (examples) - Smooth Input - fixes stuck keys, slow input and sound lag by setting correct thread priorities
 * FPS control

- Load Far - loads the world chunks at distance Far, allows fast render distance switching - Preloaded Chunks - defines an area in which no new chunks will be loaded - Chunk Updates per Frame - allows for faster world loading - Dynamic Updates - loads more chunks per frame when the player is standing still
 * Chunk Loading Control

- Clouds - Default, Fast, Fancy - Cloud Height - from 0% to 100% - Trees - Default, Fast, Fancy - Grass - Default, Fast, Fancy - Water - Default, Fast, Fancy - Rain and Snow - Default, Fast, Fancy - Sky - ON, OFF - Stars - ON, OFF - Depth Fog - ON, OFF - Weather - ON, OFF
 * Configurable Details

- Water Animated - OFF, Dynamic, ON - Lava Animated - OFF, Dynamic, ON - Fire Animated - OFF, ON - Portal Animated - OFF, ON - Redstone Animated - OFF, ON - Explosion Animated - OFF, ON - Flame Animated - OFF, ON - Smoke Animated - OFF, ON - Void Particles - OFF, ON - Water Particles - OFF, ON - Rain Splash - OFF, ON - Portal Particles - OFF, ON - Dripping Water/Lava - OFF, ON - Terrain Animated - OFF, ON - Items Animated - OFF, ON
 * Configurable animations

Switch the current Texturepack without leaving the world
 * Fast Texturepack Switching

Configurable fullscreen resolution
 * Fullscreen Resolution

- Fast Debug Info - removes lagometer from debug screen - Debug Profiler - removes profiler from debug screen
 * Debug

Default, Day Only or Night Only - works in only in Creative mode
 * Time Control

- Configurable Autosave interval - A fix for the famous Lag Spike of Death
 * Autosave