...I'm going to make some videos. They will be of someone talking. They will be made indoors with no other distracting sounds that need to be blocked out...
I use a Rode NTG-2, Rode VideoMicPro, Zoom and Tascam field recorders and several wireless lavs inc'l Sennheiser G3. For your situation I would not recommend a shotgun mic, whether camera-mounted or boom-mounted. Rather I'd suggest a Canon WM-V1 wireless "lipstick" mic: http://shopper.cnet.com/headphones-headsets/canon-wm-v1-wireless/4014-6468_9-34581063.html
It's only about $210, and produces great sound. You may not need wireless right now, but it's a big convenience and you'll end up using it much more than a cheap wired mic.
Contrary to popular belief, the strength of a shotgun mic is NOT sensitivity. They are not like an audio telescope. Rather they're good at rejecting unwanted noise. The goal in positioning a shotgun is put the broad side toward the noise. Thus you see them positioned at 45-60 deg. below the subject pointing up, or 45-60 deg. above the subject pointed down. Shotguns often have a rear pickup lobe which picks up unwanted sound from the rear -- another reason for the 45 deg. aiming convention.
In a room without much noise there are still often acoustic issues -- echoes, etc. This produces a hollow, cheap, "amateur camcorder"-type sound. Getting the mic close to the subject is the answer. This can be wired, wireless, shotgun, lav, etc. However of all these I find the wireless lav or even the Canon WM-V1 is often the most convenient.
Another approach is a separate audio field recorder. A Tascam DR-08 is only about $90, and works much better than an on-camera mic. However you have to position it *close* to the subject, keep it out of the frame, etc: http://www.amazon.com/Tascam-DR-05-Portable-Digital-Recorder/dp/B004OA6JW0
Then in post you must sync the audio and video.
Make sure you monitor the audio with earphones or headphones when recording. Ideally use manual input audio gain, if your camera supports that. Auto gain control on audio often causes clipping, flat-topping, and ramps up gain during pauses in speaking which increases background noise.
Sound is critically important in video. If you think about old grade C low-budget movies, poor audio is the main tipoff of the low production value. To paraphrase Yogi Berra, video may be 90% visual but the other half is audio. Viewers are actually more accepting of poor quality video than poor audio.