Switching to the new "Einheitstarif" costs € 5 and can be done through their website. Therefore go to "Mein simyo", where you'll find the option "Tarif einstellen" and chose "simyo Einheitstarif".
simyo is still one of the cheapest prepaid providers over here. Only Fonic (9 ct/min) and simply "easy prepaid" (8,5 ct/min) are cheaper and congstar and Bildmobil (both 10 ct/min) are almost at the same pricing level.
Fonic are using the O2 network (with T-Mobile roaming in some rural areas) and also charge data with € 0,24/MB like simyo, but don't admit users to their 3G-network and they bill GPRS in 100KB-units, so they're less attractive for data. Beyond that they require a German bank account, why they don't come into question for most of you.
simply "easy prepaid" are using the T-Mobile network, but messages are more expensive (15 ct/min), volume-based data tariffs are incredibly expensive (€ 19,00/MB) and the alternative of paying 9 ct/min for data connections isn't attractive in my eyes, too. Allthough users can access T-Mobile's 3G-network, HSDPA is not available to simply customers. Further they also require a German bank account for recharging.
Bildmobil (a subsidy of the "Bild"-tabloid) works on the Vodafone network with its' very good coverage, charges € 0,14 per message and offer free access to their WAP-portal. Beyond it all WAP- and webpages are charged € 0,35/MB in 10KB-units, but the data tariff is limited to WAP/web and handset-usage only. So you can neither use eMail or instant messaging nor get on the internet through a computer.
congstar "prepaid" (a Deutsche Telekom subsidy) operates on T-Mobile's network and charges € 0,10 for calls as well as for messages. Internet access costs € 0,49/MB, is billed in 10KB-units and is unrestricted. Users are admitted to the 3G-network, but HSDPA isn't available to congstar customers. A big advantage of congstar is, that T-Mobile supports EDGE and that they provide very good coverage.
Another interesting prepaid SIM is
Solomo, who use the E-Plus network through the only real German MVNO called vistream. Solomo offers calls to German landlines for 8 ct/min, mobiles for 16 ct/min and messages for 14 ct (even international ones). Data costs € 0,24/MB and is charged in 10KB-units. Beyond cheap roaming rates (incoming call in most European countries € 0,10/min) they offer very cheap international calls from Germany (European and North American landlines for only 9 ct/min). Also interesting is the discount you'll get for a certain month, if you exceed € 10 of revenue (-10%) and € 20 (-20%). Beyond that they're developing a VoIP-service, so you can not only place outgoing calls at attractive rates through VoIP, but receive calls on your solomo mobile number for free worldwide through VoIP!
All in all simyo perhaps is still a good choice in terms of pricing, but solomo is also very interesting for those calling abroad. However the E-Plus network, which simyo and solomo use, has been reported to be congested in urban areas in the past, so users experienced analoge modem speeds even on E-Plus' 3G-network. Also their coverage is worse than T-Mobile's and Vodafone's, especially their 3G-coverage is the worst of all German operators.
Depending on your requirements you may consider using congstar, who charge data twice as much, but have perfect GSM- and 3G-coverage and support EDGE.
Regarding a further price drop, which Deutsche Telekom's CEO Obermann threatend today, there's little scope in the mobile market, as IC-tariffs amount to € 0,0792 for T-Mobile/Vodafone and € 0,088 for E-Plus/O2. Maybe mobile-to-landline tariffs will decline, but I don't think there'll be significant change in the mobile-to-mobile-tariffs.