I'm running a campaign right now in an Ice Age setting, with a number of homebrewed monsters; I'll go through my adventure notes from the low levels tonight and see what I can rustle up for you. I know I made up stats for a saber-toothed tiger, and there might be a couple others.
From the standard MM monsters, wolves (grey and dire) are of course the top pick - nothing says "arctic setting" quite like fighting a bunch of huge white wolves in the snow. The cave bear also works very well with a coat of white paint.
In addition to regular monsters, give some thought to incorporating natural hazards into your encounters. In an arctic setting, the world itself is a dangerous foe not to be underestimated, particularly for a low-level party. Here are some things I've either used or thought about using:
Battle during a snowstorm. The PCs are hunkered down in a small sheltered area; outside that area, the deep snow is difficult terrain (which the monsters ignore) and falling snow reduces visibility to 5 squares. Use skirmisher monsters that can attack and then fade back out into the snow - great place for wolves.
Battle on a snowfield, with crevasses hidden under the snow. PCs who step on the wrong squares fall in, taking 1d10, 2d10, or 3d10 falling damage depending on depth. Ridges of bare rock provide safe zones, but severely limit mobility for PCs not willing to move off them.
Battle on an ice-choked river during a thaw. The PCs and their opponents fight across moving ice floes that go at different speeds (for realism, they should go faster in the middle of the river and slower at the edges). If any of your players grew up in the '80s, be prepared for "Frogger" jokes.
Battle in a snowy forest. The forest is choked with deep snowdrifts. Snowdrifts are extremely difficult terrain; it takes 3 extra points of movement to move through them, and anyone subjected to forced movement in a snowdrift falls prone. Use with monsters that have push or slide abilities.
PCs can climb trees, and a PC who is in a tree can shake the branches and dump snow on a foe beneath. This is an area burst attack targeting Reflex, usable as a standard action. On a hit, the target is knocked prone and blinded until the end of the PC's next turn. Once this attack is made, that tree's branches are cleared of snow; if the PC wants to do it again, s/he must move to a different tree.
Skill challenge: Trek across the frozen wastes. At the end of each day, each character must make an Endurance check or lose a healing surge. Any character who is out of surges loses hit points equal to his or her surge value instead. Anyone reduced to zero hit points by this effect freezes to death in the night. Surges and hit points lost in this way are not recovered until the PCs are able to take an extended rest someplace warm.
In addition, each PC can attempt one additional skill check per day:
- Perception: Find a sheltered place to camp (+2 to everyone's Endurance checks for that day).
- Nature: Help the party make better time (add one-third to the distance covered that day).
- Athletics: Break trail for the rest of the party (+2 to everyone else's Endurance and Nature checks for that day).
- Healing: Help a weakened companion survive the cold (+6 to one other PC's Endurance check for that day).
No matter how many skill checks are made, each of the above benefits can be gained only once a day for the entire party. (However, Healing can be used on more than one character.)
For best results, include one or two combat encounters during the journey, to break up the monotony of constant skill checks.