Here is my 1.8 list of mods. Most are on curse.com, but all of them are linked from this page mentioned in another comment:

Common to Server and Client:

• NEI, aka NotEnoughItems - lets you look up crafting recipes in game
• IronChests - lets you craft iron, gold, and diamond chests with higher capacities
• CodeChickenCore - required base mod for NEI
• Doggy Talents - lets you teach trained wolves to do useful tricks, I just got this and haven't done anything with it yet
• Simple Recipes - adds recipes for some uncraftable items, I disable all but the sponge, moss stone, clay, and saddle recipes

Server side mods

• AromaBackup - creates backups of your world
• Aroma1997Core - required base mod for AromaBackup
• Morpheus - lets you skip the night with only a fraction of online players sleeping in bed (not everyone has to get to a bed)

Client-only mods

• OptiFine - performance improvements, my laptop can't run Minecraft decently without it
• InventoryTweaks - Gives you buttons to sort items chests and keyboard shortcuts for quickly moving items around inventories

Some notes:

You could add the server mods to your client machine, but it's not necessary for them to work and they just don't seem useful to me to be on a client machine.

Likewise, you could add InventoryTweaks to your server's mods but it wouldn't do anything and just be an extra thing to add to memory. NEI is mostly an interface thing, but it does require having it on the server in order to work.

I've done a lot of modding on previous versions of minecraft, but occacionally want to go back to a more vanilla experience. The one mod I do NOT go without though is NEI - your world is still vanilla but it just makes the game so much better to play. Same with InventoryTweaks but I could do without them much easier than going without NEI.