Dylansbob 

I live in a fairly hilly city and have started using an old Burley Cub trailer for errands. Right now, I've been using the same bike for light-to-medium trips with front and rear racks and then the trailer for multiple cat litter purchases. My gearing is 45/30 and a 12/32 cassette. I'm thinking of dropping my granny to make using the trailler easier, but not having it be so low that I'm crossover gearing backwards when I drop into it.

Smallwheels

My gearing isn't low enough sometimes. I've got a triple in the front. I've seen many mountain bikes with a small chain ring with just twenty-two teeth. Maybe a triple crank set would be better for you. A Megarange cassette has a low gear with thirty-four teeth. I don't know which would be cheaper for you to get.

Singlespeed92

Yep,LOTS of mtn bikes run a 22t front granny,and 32-34t rear,and it's getting more and more popular on 29er's to run a 36t granny out back. I run 32x24 (pretty low by mtn SS standards) on my mtn 29er SS,but my former local trails were pretty hilly,and a 22/32 double front with a 11-34t rear 9 speed on my geared mtn bike.

On my CX bike (my goto in town),I run a touring triple (26/36/46) up front,but a mtn 9 speed cassette out back with 11-34t. So far(just moved here a few months ago,and due to spinal injuries,I don't get to ride everyday...just not up to it some days),my granny gear combo being 26t front/34t rear has been plenty low enough for the moderate hills we have,but I haven't hauled much weight yet,let alone a trailer.

But yeah,you have lots of options depending on your frame

Sixty Fiver

I have many bikes that range from ss/fg to 27 speeds but the main commuter and tow vehicle has a 28/38/48 triple and a 13-30 6 speed with a 3/3 split in that the bottom 3 and top 3 have a slightly wider gap between them to give closer steps at both ends of the cassette range. The 28/30 gives me a 24 gear inch low.

The extrabike has a 28/34 to give a 21 gear inch low.

The touring bike has a 28/34 and the mountain bikes have 24/34 and 24/30 which gives me some truly stump pulling gearing although these uber low > 2 gear inches are for climbing on the trails and are not anything I would need for utilitarian purposes.

For geared bikes that do not carry or tow a 40-100 range is more than sufficient.

gerv 

I use my trailer with a 44-33-22 MTB crankset. Cassette is a 7 speed. I think 28 is the big cog. Really great for making the hill back home from the grocery store.

chasm54

I ride a number of bikes. The FG is a 42/16, roughly a 70-inch gear. The road bikes use compact 50/34 chainrings and 12/25 and 12/27 cassettes. The tourer uses a Rohloff hub, again with a 42/16 ratio. It has 26" wheels, so that gves it roughly a 19" to 100" range.

wahoonc

My gear ranges are from 21" low on my expedition bike to a 40" or so on my 3 speeds. I have one single speed that is geared to around 64". For heavy hauling anything under 30" works for me. The terrain around here is gently rolling hills with only a couple of short steep ones.

Aaron

Torrilin

My low is around 33", my high is around 85". I don't mind walking up hills tho. If I routinely hit one of the (very rare) 5% grades in Madison, I'd probably have more like a 20" low.

Llamero

I have a standard 27-speed mountain bike configuration. I have an Xtracycle mounted on it, and commute with my wife and our lunches on the back for a total weight of about 350 pounds all together (myself, the wife, the lunches, and the bike). There are two hills on the mile and a half to work, both averaging around an 8% grade with one peaking out at a 10% grade. The total distance is 1.5 miles and the total climbing is 80-100'.

I have found that the second chain ring is best in a 2-4 configuration, and dropping down to 2-2 on the 10% grade, while maintaining a high cadence. The thing I've learned about hills on bicycles (and this is especially true with heavy loads) is that if you go too low of a gear, things just get harder, because you're exerting for such a longer period of time with no recovery. Therefore, I found it is best to use the gear where you're at peak exertion, but still maintaining a good cadence (don't start lagging or you'll hurt your knees).

Another thing to consider if you're having a hard time hauling loads would be an electric system. We have a BionX system that we use in the winter to assist in riding through snow and it works great. Since it has a torque sensor, the motor is completely hands free - if you need more power from the motor, just pedal harder. The regen braking is also very nice in winter, as it is basically anti-lock braking, and worked well enough such that I never actually had to use the actual brakes.

Shameful product placing, I know, but this is the configuration we've been using for around three years now and it works great.

Booger1

20x34 on 700c

Hayduke865

I swapped the granny chainring out for a 20-tooth, so with a 28 in the rear & 26" tires my low end is 18.6". On the next bike I'll be dropping that a bit further for touring and general load hauling and mountain climbing. Nothing's flat here and there are a few (avoidable) 20 degree hills where it's hard to keep the front wheel on the ground climbing in the saddle and no shortage of 10+ degree climbs on my regular routes. I like to keep spinning up hills and my knees don't need the abuse of a taller gear.

storytime

71" My main bike is a singlespeed set up with a 42x16 and 38mm knobbies. Most of the hills that I go up on a regular basis aren't too steep so it works out alright. I am thinking that I will drop down to a 66/67" once I have to start riding on snow covered roads.

gerv 

I think 42 by 16 is a very common gear for most riders... at least on the flats. That where I ride my bike most of the time. On windy days I might move to the next sprocket up on the rear cassette though.

JeanSeb

I'm running a 1x7 set-up on my commuter right now that consists of a 38t chainring and a 11-30 casette. 38-30 does feel tall sometimes when riding trails but is fine for commuting. Also, whenever 38-11 is too small, I just coast.