Use fewer enemy controllers and leaders. Especially elite and solo controllers can be devastating for a small party without a leader.
Use more minions. Minions are always a safe bet.
Focus fire on defenders. Defenders are built to take on a beating. This makes it easier for the players. If you ignore a fighter or paladin, and go after the rogue or ranger, the PC's wont have an easy way to recover from that. So usually try to dump monster encounter and recharge powers on the defender.
Use more potions. Depending on what kind of potion they need, feel free to make up potions that heal varying amounts of hit points. A level 5 potion heals 10, a level 15 heals 25. Nothing stopping you from making a level 9 that heals 15, and a level 12 that heals 20, so you have better control over potion healing.
More defensive characters. You can go about this in two ways, either equip their armor and neck slots faster than weapon slots, or use more monsters at lower levels. The second choice also tends to spread the damage more evenly in the party, so there is less focused fire, and a lesser chance of death.
And speaking of equipment, items that grant free healing like Dwarven Armor, or items that grant free saves like Boots of Free Movement will be very helpful for the group.
If it looks like you are frequently taxing healing resources, then the encounters may simply be too difficult. Ease them up. Every now and then it's good to tax those resources, but not every encounter needs to be that close.