Ullapool is a small town and can be easily viewed on foot.
The main attraction of Ullapool is the beautiful situation it is in beside the loch and surrounded by typical west Highland scenery. The town itself is pretty and can be wandered around in half and hour or so. Most people also end up walking over to the pretty but still functioning harbour, down to the loch or up the hill behind the town that, for very little effort, provides a wonderful view over the town and over to the Summer Isles.
Ullapool is a great base for walkers and Munro-baggers - see Ullapool walks for details of many routes.
The award winning Ullapool Museum in a Thomas Telford designed church is worth visiting.
There are cruises to the nearby Summer Isles in the boat 'The Summer Queen' and, for the more adventurous, on a speedboat (a RIB).
Festivals and events Ullapool is one of the most 'happening' places in the highlands with frequent live concerts and events. Much of the best musical talents of the highlands make Ullapool a regular venue with concerts in the Ceilidh Place, Seaforth and Macphail Centre (a theatre attached to the newly built secondary school). There are also a number of annual festivals:
The Ullapool Book Festival: One of the best small book festivals around 
Loopalu: An increasingly popular rock music festival 
The Ullapool Guitar Festival: An accoustic guitar festival 
Ulapool has a number of shops and two banks (Bank of Scotland and Royal Bank of Scotland).
For the essentials: Somerfield (soon to become a Tesco supermarket):A reasonably well stocked medium sized supermarket: Latheron Lane.
Costcutter: A small supermarket in the centre of the village
Food for Thought: A local butchers and seafood restaurant next to the ferry terminal. Local quality produce including smoked fish and locally caught seafood. Recommended - shop small and local.
The Frigate: A small deli attached to the coffee shop and restaurant.
The Saturday craft and food market: In summer there is a weekly Saturday market selling crafts and local produce - organic vegetables, seafood, smoked cheese and fish, local bakery.
For the mind: Two great bookshops with a wide variety of books but specialising in Scottish books:
The Ceilidh Place book shop, attached to the hotel, cafe and restaurant
The Ullapool Bookshop,  specialising in Scottish books, General Fiction, History, Travel, books for the Great Outdoors (including walking guides, maps, climber's tales), CDs and DVDs.
For the spirit There are a number of arts and crafts shops in Ullapool.
Two very good fish and chip shops are situated just over the road from the ferry terminal. They both claim to be award winning so take your pick. Most of the pubs serve food and there are a small number of restaurants, including an Indian.
An Indian restaurant with a difference. Nice and classical spicy indians food available 7 days a week in an affordable price.
The Arch Inn on the harbour front offers a nice atmosphere and live bands.
There's a great camping and caravan site right on the shore of the Loch (Loch Broom caravan site). You can pitch right by the water and watch the Stornoway ferry come in and out of port.
The Ceilidh Place is somewhere you need to go to. It's a Hotel 'cum Restaurant 'cum Bookshop 'cum Cafe 'cum Pub 'cum Art's Venue. This place is in all the best books about Scotland and for good reason, its somewhere to get away from it all and chill out. There is great food downstairs, solace upstairs in the guest lounge, the rooms are comfy and if you are lucky you will catch one of the passing musicians downstairs in by the fire. Its Scottish without being tacky, you will find no Jimmy Hats or dodgy tartan here. See this great review that sums up the place really well.