Budget:
Ottawa Jail Hostel, 75 Nicholas Street (across the street from the Rideau Centre), ? 613-235-2595 (toll free: 1-866-299-1478, fax: 613-235-9202). A member of Hostelling International, this hostel is in the old Ottawa Jail; the bedrooms are actually old jail cells. It's close to the Byward Market and downtown. Tours available. $24.15/dorm for HI members, $28.35 for non. 

Ottawa Backpackers Inn, 203 York Street, ? 613-241-3402 (toll free: 1-888-394-0334). Part of Backpackers Hostels Canada, includes kitchen, free wireless internet and free coffee/tea. In a converted house. The staff and the atmosphere are very friendly. $24/night for regular dorm beds, more for semi-private and private rooms.  edit
Barefoot Hostel, 455 Cumberland St, 613-237-0335. A clean, modern hostel located downtown. Included for use is a mini-kitchen, back patio with lounge chairs, common room with a huge HDTV, computer (with internet), free WiFi, plush bed linens, lockers and three shared bathrooms. There is also an "Xbox Station," where up to four people can play Xbox live. Rates start at $38/night/per person and you can book online. Make sure to check their website or twitter page for current promotions.

Mid-range:
Albert at Bay Suite Hotel, 435 Albert Street (corner of Bay St.). The building is nicely located downtown within easy walking distance of the main attractions, shops and restaurants. The hotel itself is a converted apartment building where you'll find large one and two bedrooms suites. Rates range from $119/night to $229/night for the one and two bedroom suites respectively.
Albert House Inn, 478 Albert Street. The house is old but kept well, the people are very nice and the breakfast is generous. The bedrooms are clean and cosy and you can borrow books and newspapers.
Auberge King Edward Bed and Breakfast, 525 King Edward Avenue (downtown beside the University of Ottawa and a 5 minute walk from the Rideau Canal). Well-preserved Victorian architecture packed with character. Free parking and WIFI. $90-120 (plus taxes). 

Avalon Bed and Breakfast, 539 Besserer St (Near Rideau and Charlotte), ? +1 613 241-6403. checkin: 1PM; checkout: 11AM. A well reviewed downtown Ottawa Bed and Breakfast. Turn of the century home with modern decor. A 15 minute walk to the BiWard Market. Free parking and WIFI. $75-$125. 
Best Western Victoria Park Suites, 377 O'Connor St. (near Elgin St.). The hotel is downtown near the Museum of Nature. $100 (and up).

The Bostonian - Executive Suites, 341 Maclaren St. Centrally located contemporary boutique hotel offering apartment style suites and terrific service. Rates start at $104.

ByWard Blue Inn, 157 Clarence Street. Welcome to Ottawa's only B & B hotel in the picturesque ByWard Market. This charming inn offers people traveling for business or pleasure fantastic room rates in a great location. $79-149

Cartier Place Suite Hotel, 180 Cooper Street. Features unique pet friendly downtown suite lodging accommodations minutes from Parliament Hill. Discover unique studios, one or two bedrooms, and VIP suites with Jacuzzis, close to tourist attractions.

Comfort Inn Ottawa West (Kanata), 222 Hearst Way (This convenient Ottawa West location is only 5 min from Scotiabank Place and offers guests excellent value including free breakfast, free parking, and free internet. 20 min from Downtown, Highway #417, Exit 138 Eagleson Road), ? 613-592-2200 ( fax: 613-591-9600). checkin: 11:00; checkout: 15:00.  edit

Novotel Hotel located across the street from the east side of the Rideau Centre on Nicholas Street. Modern hotel with an emphasis on energy conservation. Modern restaurant and banquet facilities. This location has free internet kiosks in the main lobby open to the public.

Sheraton Ottawa Hotel, 150 Albert St, ? +1 866 716-8101. checkin: 3PM; checkout: 12PM. Sheraton Ottawa Hotel is located in the heart of downtown - steps from Parliament Hill, the National Gallery, and other major attractions. Each room features the signature Sheraton Sweet Sleeper bed, and the lobby connectivity hub offers complimentary internet and PC workstation use. $109 and up. 

Shirley Samantha's Bed & Breakfast, 28 Carlotta Avenue (From Hwy. 417 take Exit 117 Vanier Parkway; north on Vanier Parkway to McArthur Avenue, left on McArthur to Marguerite Avenue, left on Marguerite. Then right on Carlotta Avenue.), ? 613-745-2105. checkin: as arranged; checkout: 11 a.m.. On a quiet residential street, within walking distance from downtown and half a block from the Rideau River cycling/walking path. Two queen-bedded rooms, one with ensuite, the other with private bath. Centrally air conditioned, complimentary parking, snacks and WiFi. Delicious breakfasts featuring home baking. $70-$120 per night. 

University of Ottawa located within a quick walk to Rideau Centre and downtown, the university runs a guest house with private rooms in one of its newer housing complexes. As of May 2005, the rate for a single was $90 with a discount for University of Ottawa students.

The Black Lab Inn Welcome to Ottawa's only truly dog friendly bed & breakfast. Located in the south end of Ottawa with plenty of places to take your dog to play and walk with the Rideau River just down the street. Delicious full breakfasts with all the amenities to cater to guests and their dogs.

Gasthaus Switzerland Inn, 89 Daly Ave, (Beautiful Historic 1872 Small Hotel Right Downtown), 613-237-0335. A charming, cosy small hotel located in the heart of Ottawa, features 22 rooms including 2 honeymoon suites. The Inn was built in 1872 from limestone in a 19th Century Vernacular Classical Revival. Gasthaus offers traditional Swiss hospitality, with modern comfort. Free Wi-Fi and free internet computer desk in the common area for guests. Delicious buffet breakfast is included with Bircher-Muesli and fresh ground Swiss espresso. Discount available for government employees & university professors.

Splurge:

The Ottawa Marriott Hotel, 100 Kent St (near Parliament Hill), ? +1 613 238-1122 (toll free: +1 800 853-8463). The Ottawa Marriott Hotel is in downtown Ottawa one block from the Parliament Buildings and steps away from museums and shopping. This Ottawa hotel includes a revolving restaurant, Kids' Zone as well as an indoor pool, sauna and fitness centre. $154+. 

Arc, Slater Street (near Parliament Hill). A trendy boutique hotel with prices to match its style.

Chateau Laurier, (near Parliament Hill). The city's grand old hotel: its oldest and most famous luxury hotel as well as one of its landmarks. Rooms facing west overlook the Rideau Canal locks and have stellar views of the Parliament buildings.

The Westin Ottawa, 11 Colonel By Dr (near Parliament Hill), ? +1-866-716-8101. checkin: 3pm; checkout: 12pm. This newly renovated hotel is also connected to the Rideau Centre and the soon to open Ottawa Convention Centre by a walkway. It is steps from Parliament Hill and the Byward market and each of the 496 rooms features the ten-layer Heavenly Bed. Rates start at $159 / night. 

The Delta Ottawa Hotel. 361 Queen Street. Located downtown, a few blocks west of Parliament Hill, near the Supreme Court of Canada. The outside decor is not much to look at but the one and two bedroom rooms are spacious and have kitchenettes, comfortable for a longer stay. Rates for standard hotel rooms start at $159 / night.

Lord Elgin  is centrally located on Elgin Street across from the National Arts Centre, a stone's throw from Parliament Hill, and is one of Ottawa's two classic hotels (the other being the Chateau Laurier). It has recently been upgraded. While it has "splurge" rates, most rooms are reasonably priced. Good value, and a Starbucks off the lobby.

The Brookstreet  in Kanata is a newer luxury hotel and resort popular with technology companies and visiting sports teams. Facilities include a full-service spa with 11 treatment rooms, a championship golf course (The Marshes), a European PGA-approved short course (Marchwood), a four-diamond restaurant (Perspectives) and a fitness studio with whirlpools, steam rooms and indoor and outdoor pools.