I'll start with the following;

Doctor Who
Torchwood
Smallville
Supernatural
Heroes

Lol, I suggested one of those. I will second Doctor Who.

You may also like:

Charmed
Roswell
Dark Angel
Alias

FIREFLY!

Or is that a given?

Outside of the Whedonverse, I'd err, third Doctor Who and Torchwood (even though everyone knows Torchwood is crap, haha--but it's good fun).

And I'd also say anything with clever and witty dialogue, like Friends, Monty Python, Jeeves and Wooster...

Idk, Buffy is just such a complete world, and it's such a rich tv show, there's so many different things to like. I can't really think of any tv show like it.

Torchwood has James - thus it could be a pig wearing a fake mustache and I would view it.

Well, I have been trying to get some of you to watch Battlestar for ages, lol. But in all honestly, I can see why that show seems like a project. I didn't want to watch it at first either. The only Buffy fan I know of that has branched out so far is Debs, and she's really really enjoying it. But I'm not sure if I can make the blanket statement that if you're Buffy fan, you'll like Battlestar. Maybe I could say if you're an Angel fan you will, but I'm not sure. You have to like the drama and scifi aspects to appreciate it.

For those fans that appreciate the darker sides of Buffy, I would highly recommend a show called Carnivale. It's not easy to find and it played on HBO but it does have a spot here on Fanpop that has some episodes available. It's very very dark, but it is also very supernatural and very worth watching.

I think the biggest blanket statement I could make would be Veronica Mars. In a lot ways, I think it has the most in common with Buffy. Strong female lead (veronica is actually probably more likable than Buffy Summers), great witty dialogue, pop culture references, and mystery.

So the three I can say for sure are:
1. Battlestar Galactica: If you like really good storytelling and lots of drama, with a hint of sci fi thrown in.

2. Carnivale: For supernatural storytelling with really really dark themes.

3. Veronica Mars: For the teen friendly, strong female, great dialogue having dramedy.

I'll second Veronica Mars.

I've got Battlestar on the list to watch, so I'm sure I'll like it.

And I probably would as well Arabella, lol. In fact, someone said something a bit like that to me the other day.

I keep putting it off Nose, I'll have it up, ready to go and then it just seems daunting and I don't know why. It just looks like a big show. I did hear it was ending this season (this season being the last) so atleast I'll get it all instead of having to wait for upcoming season.

i second charmed i love it! it also has strong female leads who stuggle with their supernatural destiny and who have dabbled in the dark side of things have difficulty finding love (except piper who has trouble hanging onto it) what i think is a witty dialoge,has obviously supernatural elements but its great

Veronica Mars for sure you'd enjoy.

I haven't seen it yet but I have heard of a new vamp show called "True blood", would this show appeal to buffy fans?

I'm not sure, depends, Moonlight didn't appeal to a lot of us.

I saw a promo for Moonlight, then read that the producers said it was NOTHING like Angel. I was peeved.

I saw one episode of Trueblood and even though I like Anna Paquin I was not impressed with the show. Maybe it gets better as the season goes on?

I agree, True Blood is not very impressive. It does however, have a campy kind of charm all its own. I'm not saying it's good, but it's somewhat entertaining.

Also, I have to add that I definitely second Supernatural. They even give a shout out to Buffy at one point.

I do realise this isn't really genre related to Buffy but How I Met Your Mother, with Aly, is amazing, though I do suggest you get into atleast season two before judging.

I have found myself also liking Charmed,Heroes,Doctor Who,Dollhouse,Reaper,and Legend of the Seeker. I watched one episode of TrueBlood and did not like it and I did not like Torchwood as much as i like Doctor Who (even with James showing up in one or two episodes...seeing him making out with Captain Jack just was not what I wanted to see)

I would recommend The X-files, Xena: Warrior Princess, maybe Merlin and Bones.

I really enjoy Lost Girl which I think is similar to buffy.

I second Charmed and Battlestar and will add to the list the Stargate Series. It has three shows so far, Stargate SG-1, Stargate Atlantis, and Stargate Universe.

IF YOU ARE FROM THE UK OR HAVE BBC AMERICA THEN YOU CAN TRY BEING HUMAN - IT'S ABOUT VAMPIRES, GHOSTS, WITCHES AND WEREWOLVES. ETC. AND IF YOU DON'T REALLY LIKE THAT THEN THERE IS ALWAYS:

NIKKITA
REVENGE
FRIENDS
CHARMED

Do I even have to say angel?

Torchwood that I believe has james marsters in it although in shown in different colours
Doctor who
Merlin (the BBC version) do you get that in America?
Primeval
And Miranda because... Its amazing

The X-Files was my favorite show for 17 years. I never thought I could love another show as much until I discovered Buffy in 2010. Now I must say that Buffy is my new favorite. Other similar shows I love include:

Angel (Of course!)
Dawson's Creek (Smart and witty dialogue, very Weadonesque writing. Not sci-fi though.)
Roswell (Like a cross between Dawson's Creek and The X-Files.)
Supernatural (Really feels like it could take place inside the Angel universe.)

Also...
Heroes
Threshold
Tru Calling
...maybe not the greatest series', but definitely some amazing episodes. These shows could have been truly great.

Whedon Shows: Firefly, Dollhouse
Shows with a kickass group of friends who compose a family: Leverage, Community
Shows with a female heroine/main character: Dead Like Me, Tru Calling, Veronica Mars
SciFi/Supernatural series: Pushing Daisies, The Walking Dead, Going Postal

Comedies great groups of friends: Friends, HIMYM
Friends that face serious problems together: Pretty Little Liars, Vampire Diaries (both of these have great plot writing)

True Blood was mentioned above. I never liked the show, but the books were great.

I really love Buffy but you should definitely watch

The originals(starts of slow but after a few episodes its amazing)
Pretty little liars,
iZombie,
The 100,
And shadowhunters(tho it hasn't come out yet I have a good feeling about it)