here are the top 5 Mods from trusted websites.
1. optifine anti-lag
2. shaders
3. icbm electricity
4. buildcraft
5. computer craft
here are images of all of them except #1
Shaders Mod. It adds a rather-realistic look to Minecraft. It adds moving trees, grass(not blocks) Wind and makes the water move as if it it was real.
ICBM Electricity. It adds a whole-lot of TNT like nuclear and cluster bombs. Adds missiles so you can target anywhere you want in your Minecraft mod. Very Realistic.
BuildCraft. Adds a whole-lot of new blocks like in constructing sites. Can help with your building skills. Adds a bunch of Factory-like blocks and they do have functions. Alot of people say it's and awesome mod.
Computer Craft. Adds a lot of technical things that could help you build your dream home in Minecraft. Infact, you can actually browse on the computer (added by the mod) in game! But that's not it! You can add command blocks when once triggered by redstone, do any commands you want. The mod adds a lot of commands to play around with.